![Darren Hart](/assets/img/avatar_default.png)
When requeuing tasks from one futex to another, the reference held by the requeued task to the original futex location needs to be dropped eventually. Dropping the reference may ultimately lead to a call to "iput_final" and subsequently call into filesystem- specific code - which may be non-atomic. It is therefore safer to defer this drop operation until after the futex_hash_bucket spinlock has been dropped. Originally-From: Helge Bahmann <hcb@chaoticmind.net> Signed-off-by: Darren Hart <dvhltc@us.ibm.com> Cc: <stable@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Dinakar Guniguntala <dino@in.ibm.com> Cc: John Stultz <johnstul@linux.vnet.ibm.com> Cc: Sven-Thorsten Dietrich <sdietrich@novell.com> Cc: John Kacur <jkacur@redhat.com> LKML-Reference: <4AD7A298.5040802@us.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2651 lines
68 KiB
C
2651 lines
68 KiB
C
/*
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* Fast Userspace Mutexes (which I call "Futexes!").
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* (C) Rusty Russell, IBM 2002
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*
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* Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
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* (C) Copyright 2003 Red Hat Inc, All Rights Reserved
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*
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* Removed page pinning, fix privately mapped COW pages and other cleanups
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* (C) Copyright 2003, 2004 Jamie Lokier
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*
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* Robust futex support started by Ingo Molnar
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* (C) Copyright 2006 Red Hat Inc, All Rights Reserved
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* Thanks to Thomas Gleixner for suggestions, analysis and fixes.
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*
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* PI-futex support started by Ingo Molnar and Thomas Gleixner
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* Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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* Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
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*
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* PRIVATE futexes by Eric Dumazet
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* Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
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*
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* Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
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* Copyright (C) IBM Corporation, 2009
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* Thanks to Thomas Gleixner for conceptual design and careful reviews.
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*
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* Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
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* enough at me, Linus for the original (flawed) idea, Matthew
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* Kirkwood for proof-of-concept implementation.
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*
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* "The futexes are also cursed."
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* "But they come in a choice of three flavours!"
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*/
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#include <linux/slab.h>
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#include <linux/poll.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/jhash.h>
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#include <linux/init.h>
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#include <linux/futex.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/syscalls.h>
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#include <linux/signal.h>
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#include <linux/module.h>
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#include <linux/magic.h>
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#include <linux/pid.h>
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#include <linux/nsproxy.h>
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#include <asm/futex.h>
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#include "rtmutex_common.h"
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int __read_mostly futex_cmpxchg_enabled;
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#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
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/*
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* Priority Inheritance state:
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*/
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struct futex_pi_state {
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/*
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* list of 'owned' pi_state instances - these have to be
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* cleaned up in do_exit() if the task exits prematurely:
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*/
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struct list_head list;
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/*
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* The PI object:
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*/
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struct rt_mutex pi_mutex;
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struct task_struct *owner;
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atomic_t refcount;
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union futex_key key;
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};
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/**
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* struct futex_q - The hashed futex queue entry, one per waiting task
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* @task: the task waiting on the futex
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* @lock_ptr: the hash bucket lock
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* @key: the key the futex is hashed on
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* @pi_state: optional priority inheritance state
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* @rt_waiter: rt_waiter storage for use with requeue_pi
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* @requeue_pi_key: the requeue_pi target futex key
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* @bitset: bitset for the optional bitmasked wakeup
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*
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* We use this hashed waitqueue, instead of a normal wait_queue_t, so
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* we can wake only the relevant ones (hashed queues may be shared).
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*
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* A futex_q has a woken state, just like tasks have TASK_RUNNING.
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* It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
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* The order of wakup is always to make the first condition true, then
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* the second.
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*
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* PI futexes are typically woken before they are removed from the hash list via
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* the rt_mutex code. See unqueue_me_pi().
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*/
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struct futex_q {
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struct plist_node list;
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struct task_struct *task;
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spinlock_t *lock_ptr;
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union futex_key key;
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struct futex_pi_state *pi_state;
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struct rt_mutex_waiter *rt_waiter;
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union futex_key *requeue_pi_key;
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u32 bitset;
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};
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/*
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* Hash buckets are shared by all the futex_keys that hash to the same
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* location. Each key may have multiple futex_q structures, one for each task
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* waiting on a futex.
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*/
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struct futex_hash_bucket {
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spinlock_t lock;
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struct plist_head chain;
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};
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static struct futex_hash_bucket futex_queues[1<<FUTEX_HASHBITS];
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/*
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* We hash on the keys returned from get_futex_key (see below).
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*/
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static struct futex_hash_bucket *hash_futex(union futex_key *key)
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{
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u32 hash = jhash2((u32*)&key->both.word,
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(sizeof(key->both.word)+sizeof(key->both.ptr))/4,
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key->both.offset);
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return &futex_queues[hash & ((1 << FUTEX_HASHBITS)-1)];
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}
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/*
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* Return 1 if two futex_keys are equal, 0 otherwise.
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*/
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static inline int match_futex(union futex_key *key1, union futex_key *key2)
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{
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return (key1 && key2
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&& key1->both.word == key2->both.word
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&& key1->both.ptr == key2->both.ptr
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&& key1->both.offset == key2->both.offset);
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}
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/*
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* Take a reference to the resource addressed by a key.
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* Can be called while holding spinlocks.
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*
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*/
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static void get_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr)
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return;
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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atomic_inc(&key->shared.inode->i_count);
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break;
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case FUT_OFF_MMSHARED:
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atomic_inc(&key->private.mm->mm_count);
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break;
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}
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}
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/*
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* Drop a reference to the resource addressed by a key.
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* The hash bucket spinlock must not be held.
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*/
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static void drop_futex_key_refs(union futex_key *key)
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{
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if (!key->both.ptr) {
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/* If we're here then we tried to put a key we failed to get */
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WARN_ON_ONCE(1);
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return;
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}
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switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
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case FUT_OFF_INODE:
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iput(key->shared.inode);
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break;
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case FUT_OFF_MMSHARED:
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mmdrop(key->private.mm);
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break;
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}
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}
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/**
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* get_futex_key() - Get parameters which are the keys for a futex
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* @uaddr: virtual address of the futex
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* @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED
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* @key: address where result is stored.
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* @rw: mapping needs to be read/write (values: VERIFY_READ,
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* VERIFY_WRITE)
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*
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* Returns a negative error code or 0
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* The key words are stored in *key on success.
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*
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* For shared mappings, it's (page->index, vma->vm_file->f_path.dentry->d_inode,
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* offset_within_page). For private mappings, it's (uaddr, current->mm).
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* We can usually work out the index without swapping in the page.
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*
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* lock_page() might sleep, the caller should not hold a spinlock.
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*/
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static int
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get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
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{
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unsigned long address = (unsigned long)uaddr;
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struct mm_struct *mm = current->mm;
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struct page *page;
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int err;
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/*
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* The futex address must be "naturally" aligned.
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*/
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key->both.offset = address % PAGE_SIZE;
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if (unlikely((address % sizeof(u32)) != 0))
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return -EINVAL;
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address -= key->both.offset;
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/*
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* PROCESS_PRIVATE futexes are fast.
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* As the mm cannot disappear under us and the 'key' only needs
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* virtual address, we dont even have to find the underlying vma.
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* Note : We do have to check 'uaddr' is a valid user address,
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* but access_ok() should be faster than find_vma()
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*/
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if (!fshared) {
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if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
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return -EFAULT;
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key->private.mm = mm;
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key->private.address = address;
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get_futex_key_refs(key);
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return 0;
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}
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again:
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err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page);
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if (err < 0)
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return err;
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page = compound_head(page);
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lock_page(page);
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if (!page->mapping) {
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unlock_page(page);
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put_page(page);
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goto again;
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}
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/*
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* Private mappings are handled in a simple way.
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*
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* NOTE: When userspace waits on a MAP_SHARED mapping, even if
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* it's a read-only handle, it's expected that futexes attach to
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* the object not the particular process.
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*/
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if (PageAnon(page)) {
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key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
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key->private.mm = mm;
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key->private.address = address;
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} else {
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key->both.offset |= FUT_OFF_INODE; /* inode-based key */
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key->shared.inode = page->mapping->host;
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key->shared.pgoff = page->index;
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}
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get_futex_key_refs(key);
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unlock_page(page);
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put_page(page);
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return 0;
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}
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static inline
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void put_futex_key(int fshared, union futex_key *key)
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{
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drop_futex_key_refs(key);
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}
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/**
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* fault_in_user_writeable() - Fault in user address and verify RW access
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* @uaddr: pointer to faulting user space address
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*
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* Slow path to fixup the fault we just took in the atomic write
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* access to @uaddr.
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*
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* We have no generic implementation of a non destructive write to the
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* user address. We know that we faulted in the atomic pagefault
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* disabled section so we can as well avoid the #PF overhead by
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* calling get_user_pages() right away.
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*/
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static int fault_in_user_writeable(u32 __user *uaddr)
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{
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int ret = get_user_pages(current, current->mm, (unsigned long)uaddr,
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1, 1, 0, NULL, NULL);
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return ret < 0 ? ret : 0;
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}
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/**
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* futex_top_waiter() - Return the highest priority waiter on a futex
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* @hb: the hash bucket the futex_q's reside in
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* @key: the futex key (to distinguish it from other futex futex_q's)
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*
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* Must be called with the hb lock held.
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*/
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static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
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union futex_key *key)
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{
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struct futex_q *this;
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plist_for_each_entry(this, &hb->chain, list) {
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if (match_futex(&this->key, key))
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return this;
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}
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return NULL;
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}
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static u32 cmpxchg_futex_value_locked(u32 __user *uaddr, u32 uval, u32 newval)
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{
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u32 curval;
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pagefault_disable();
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curval = futex_atomic_cmpxchg_inatomic(uaddr, uval, newval);
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pagefault_enable();
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return curval;
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}
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static int get_futex_value_locked(u32 *dest, u32 __user *from)
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{
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int ret;
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pagefault_disable();
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ret = __copy_from_user_inatomic(dest, from, sizeof(u32));
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pagefault_enable();
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return ret ? -EFAULT : 0;
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}
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/*
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* PI code:
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*/
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static int refill_pi_state_cache(void)
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{
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struct futex_pi_state *pi_state;
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if (likely(current->pi_state_cache))
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return 0;
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pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
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if (!pi_state)
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return -ENOMEM;
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INIT_LIST_HEAD(&pi_state->list);
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/* pi_mutex gets initialized later */
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pi_state->owner = NULL;
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atomic_set(&pi_state->refcount, 1);
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pi_state->key = FUTEX_KEY_INIT;
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current->pi_state_cache = pi_state;
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return 0;
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}
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static struct futex_pi_state * alloc_pi_state(void)
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{
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struct futex_pi_state *pi_state = current->pi_state_cache;
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WARN_ON(!pi_state);
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current->pi_state_cache = NULL;
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return pi_state;
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}
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static void free_pi_state(struct futex_pi_state *pi_state)
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{
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if (!atomic_dec_and_test(&pi_state->refcount))
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return;
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/*
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* If pi_state->owner is NULL, the owner is most probably dying
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* and has cleaned up the pi_state already
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*/
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if (pi_state->owner) {
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spin_lock_irq(&pi_state->owner->pi_lock);
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list_del_init(&pi_state->list);
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spin_unlock_irq(&pi_state->owner->pi_lock);
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rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
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}
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if (current->pi_state_cache)
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kfree(pi_state);
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else {
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/*
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* pi_state->list is already empty.
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* clear pi_state->owner.
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* refcount is at 0 - put it back to 1.
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*/
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pi_state->owner = NULL;
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atomic_set(&pi_state->refcount, 1);
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current->pi_state_cache = pi_state;
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}
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}
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/*
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* Look up the task based on what TID userspace gave us.
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* We dont trust it.
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*/
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static struct task_struct * futex_find_get_task(pid_t pid)
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{
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struct task_struct *p;
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const struct cred *cred = current_cred(), *pcred;
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rcu_read_lock();
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p = find_task_by_vpid(pid);
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if (!p) {
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p = ERR_PTR(-ESRCH);
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} else {
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pcred = __task_cred(p);
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if (cred->euid != pcred->euid &&
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cred->euid != pcred->uid)
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p = ERR_PTR(-ESRCH);
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else
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get_task_struct(p);
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}
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rcu_read_unlock();
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return p;
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}
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/*
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* This task is holding PI mutexes at exit time => bad.
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* Kernel cleans up PI-state, but userspace is likely hosed.
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* (Robust-futex cleanup is separate and might save the day for userspace.)
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*/
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void exit_pi_state_list(struct task_struct *curr)
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{
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struct list_head *next, *head = &curr->pi_state_list;
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struct futex_pi_state *pi_state;
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struct futex_hash_bucket *hb;
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union futex_key key = FUTEX_KEY_INIT;
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if (!futex_cmpxchg_enabled)
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return;
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/*
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* We are a ZOMBIE and nobody can enqueue itself on
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* pi_state_list anymore, but we have to be careful
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* versus waiters unqueueing themselves:
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*/
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spin_lock_irq(&curr->pi_lock);
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while (!list_empty(head)) {
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next = head->next;
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pi_state = list_entry(next, struct futex_pi_state, list);
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key = pi_state->key;
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hb = hash_futex(&key);
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spin_unlock_irq(&curr->pi_lock);
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spin_lock(&hb->lock);
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spin_lock_irq(&curr->pi_lock);
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/*
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* We dropped the pi-lock, so re-check whether this
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* task still owns the PI-state:
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*/
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if (head->next != next) {
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spin_unlock(&hb->lock);
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continue;
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}
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WARN_ON(pi_state->owner != curr);
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WARN_ON(list_empty(&pi_state->list));
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list_del_init(&pi_state->list);
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pi_state->owner = NULL;
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spin_unlock_irq(&curr->pi_lock);
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rt_mutex_unlock(&pi_state->pi_mutex);
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spin_unlock(&hb->lock);
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spin_lock_irq(&curr->pi_lock);
|
|
}
|
|
spin_unlock_irq(&curr->pi_lock);
|
|
}
|
|
|
|
static int
|
|
lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
|
|
union futex_key *key, struct futex_pi_state **ps)
|
|
{
|
|
struct futex_pi_state *pi_state = NULL;
|
|
struct futex_q *this, *next;
|
|
struct plist_head *head;
|
|
struct task_struct *p;
|
|
pid_t pid = uval & FUTEX_TID_MASK;
|
|
|
|
head = &hb->chain;
|
|
|
|
plist_for_each_entry_safe(this, next, head, list) {
|
|
if (match_futex(&this->key, key)) {
|
|
/*
|
|
* Another waiter already exists - bump up
|
|
* the refcount and return its pi_state:
|
|
*/
|
|
pi_state = this->pi_state;
|
|
/*
|
|
* Userspace might have messed up non PI and PI futexes
|
|
*/
|
|
if (unlikely(!pi_state))
|
|
return -EINVAL;
|
|
|
|
WARN_ON(!atomic_read(&pi_state->refcount));
|
|
WARN_ON(pid && pi_state->owner &&
|
|
pi_state->owner->pid != pid);
|
|
|
|
atomic_inc(&pi_state->refcount);
|
|
*ps = pi_state;
|
|
|
|
return 0;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* We are the first waiter - try to look up the real owner and attach
|
|
* the new pi_state to it, but bail out when TID = 0
|
|
*/
|
|
if (!pid)
|
|
return -ESRCH;
|
|
p = futex_find_get_task(pid);
|
|
if (IS_ERR(p))
|
|
return PTR_ERR(p);
|
|
|
|
/*
|
|
* We need to look at the task state flags to figure out,
|
|
* whether the task is exiting. To protect against the do_exit
|
|
* change of the task flags, we do this protected by
|
|
* p->pi_lock:
|
|
*/
|
|
spin_lock_irq(&p->pi_lock);
|
|
if (unlikely(p->flags & PF_EXITING)) {
|
|
/*
|
|
* The task is on the way out. When PF_EXITPIDONE is
|
|
* set, we know that the task has finished the
|
|
* cleanup:
|
|
*/
|
|
int ret = (p->flags & PF_EXITPIDONE) ? -ESRCH : -EAGAIN;
|
|
|
|
spin_unlock_irq(&p->pi_lock);
|
|
put_task_struct(p);
|
|
return ret;
|
|
}
|
|
|
|
pi_state = alloc_pi_state();
|
|
|
|
/*
|
|
* Initialize the pi_mutex in locked state and make 'p'
|
|
* the owner of it:
|
|
*/
|
|
rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
|
|
|
|
/* Store the key for possible exit cleanups: */
|
|
pi_state->key = *key;
|
|
|
|
WARN_ON(!list_empty(&pi_state->list));
|
|
list_add(&pi_state->list, &p->pi_state_list);
|
|
pi_state->owner = p;
|
|
spin_unlock_irq(&p->pi_lock);
|
|
|
|
put_task_struct(p);
|
|
|
|
*ps = pi_state;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
|
|
* @uaddr: the pi futex user address
|
|
* @hb: the pi futex hash bucket
|
|
* @key: the futex key associated with uaddr and hb
|
|
* @ps: the pi_state pointer where we store the result of the
|
|
* lookup
|
|
* @task: the task to perform the atomic lock work for. This will
|
|
* be "current" except in the case of requeue pi.
|
|
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
|
*
|
|
* Returns:
|
|
* 0 - ready to wait
|
|
* 1 - acquired the lock
|
|
* <0 - error
|
|
*
|
|
* The hb->lock and futex_key refs shall be held by the caller.
|
|
*/
|
|
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
|
|
union futex_key *key,
|
|
struct futex_pi_state **ps,
|
|
struct task_struct *task, int set_waiters)
|
|
{
|
|
int lock_taken, ret, ownerdied = 0;
|
|
u32 uval, newval, curval;
|
|
|
|
retry:
|
|
ret = lock_taken = 0;
|
|
|
|
/*
|
|
* To avoid races, we attempt to take the lock here again
|
|
* (by doing a 0 -> TID atomic cmpxchg), while holding all
|
|
* the locks. It will most likely not succeed.
|
|
*/
|
|
newval = task_pid_vnr(task);
|
|
if (set_waiters)
|
|
newval |= FUTEX_WAITERS;
|
|
|
|
curval = cmpxchg_futex_value_locked(uaddr, 0, newval);
|
|
|
|
if (unlikely(curval == -EFAULT))
|
|
return -EFAULT;
|
|
|
|
/*
|
|
* Detect deadlocks.
|
|
*/
|
|
if ((unlikely((curval & FUTEX_TID_MASK) == task_pid_vnr(task))))
|
|
return -EDEADLK;
|
|
|
|
/*
|
|
* Surprise - we got the lock. Just return to userspace:
|
|
*/
|
|
if (unlikely(!curval))
|
|
return 1;
|
|
|
|
uval = curval;
|
|
|
|
/*
|
|
* Set the FUTEX_WAITERS flag, so the owner will know it has someone
|
|
* to wake at the next unlock.
|
|
*/
|
|
newval = curval | FUTEX_WAITERS;
|
|
|
|
/*
|
|
* There are two cases, where a futex might have no owner (the
|
|
* owner TID is 0): OWNER_DIED. We take over the futex in this
|
|
* case. We also do an unconditional take over, when the owner
|
|
* of the futex died.
|
|
*
|
|
* This is safe as we are protected by the hash bucket lock !
|
|
*/
|
|
if (unlikely(ownerdied || !(curval & FUTEX_TID_MASK))) {
|
|
/* Keep the OWNER_DIED bit */
|
|
newval = (curval & ~FUTEX_TID_MASK) | task_pid_vnr(task);
|
|
ownerdied = 0;
|
|
lock_taken = 1;
|
|
}
|
|
|
|
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
|
|
|
|
if (unlikely(curval == -EFAULT))
|
|
return -EFAULT;
|
|
if (unlikely(curval != uval))
|
|
goto retry;
|
|
|
|
/*
|
|
* We took the lock due to owner died take over.
|
|
*/
|
|
if (unlikely(lock_taken))
|
|
return 1;
|
|
|
|
/*
|
|
* We dont have the lock. Look up the PI state (or create it if
|
|
* we are the first waiter):
|
|
*/
|
|
ret = lookup_pi_state(uval, hb, key, ps);
|
|
|
|
if (unlikely(ret)) {
|
|
switch (ret) {
|
|
case -ESRCH:
|
|
/*
|
|
* No owner found for this futex. Check if the
|
|
* OWNER_DIED bit is set to figure out whether
|
|
* this is a robust futex or not.
|
|
*/
|
|
if (get_futex_value_locked(&curval, uaddr))
|
|
return -EFAULT;
|
|
|
|
/*
|
|
* We simply start over in case of a robust
|
|
* futex. The code above will take the futex
|
|
* and return happy.
|
|
*/
|
|
if (curval & FUTEX_OWNER_DIED) {
|
|
ownerdied = 1;
|
|
goto retry;
|
|
}
|
|
default:
|
|
break;
|
|
}
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* The hash bucket lock must be held when this is called.
|
|
* Afterwards, the futex_q must not be accessed.
|
|
*/
|
|
static void wake_futex(struct futex_q *q)
|
|
{
|
|
struct task_struct *p = q->task;
|
|
|
|
/*
|
|
* We set q->lock_ptr = NULL _before_ we wake up the task. If
|
|
* a non futex wake up happens on another CPU then the task
|
|
* might exit and p would dereference a non existing task
|
|
* struct. Prevent this by holding a reference on p across the
|
|
* wake up.
|
|
*/
|
|
get_task_struct(p);
|
|
|
|
plist_del(&q->list, &q->list.plist);
|
|
/*
|
|
* The waiting task can free the futex_q as soon as
|
|
* q->lock_ptr = NULL is written, without taking any locks. A
|
|
* memory barrier is required here to prevent the following
|
|
* store to lock_ptr from getting ahead of the plist_del.
|
|
*/
|
|
smp_wmb();
|
|
q->lock_ptr = NULL;
|
|
|
|
wake_up_state(p, TASK_NORMAL);
|
|
put_task_struct(p);
|
|
}
|
|
|
|
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *this)
|
|
{
|
|
struct task_struct *new_owner;
|
|
struct futex_pi_state *pi_state = this->pi_state;
|
|
u32 curval, newval;
|
|
|
|
if (!pi_state)
|
|
return -EINVAL;
|
|
|
|
spin_lock(&pi_state->pi_mutex.wait_lock);
|
|
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
|
|
|
|
/*
|
|
* This happens when we have stolen the lock and the original
|
|
* pending owner did not enqueue itself back on the rt_mutex.
|
|
* Thats not a tragedy. We know that way, that a lock waiter
|
|
* is on the fly. We make the futex_q waiter the pending owner.
|
|
*/
|
|
if (!new_owner)
|
|
new_owner = this->task;
|
|
|
|
/*
|
|
* We pass it to the next owner. (The WAITERS bit is always
|
|
* kept enabled while there is PI state around. We must also
|
|
* preserve the owner died bit.)
|
|
*/
|
|
if (!(uval & FUTEX_OWNER_DIED)) {
|
|
int ret = 0;
|
|
|
|
newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
|
|
|
|
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
|
|
|
|
if (curval == -EFAULT)
|
|
ret = -EFAULT;
|
|
else if (curval != uval)
|
|
ret = -EINVAL;
|
|
if (ret) {
|
|
spin_unlock(&pi_state->pi_mutex.wait_lock);
|
|
return ret;
|
|
}
|
|
}
|
|
|
|
spin_lock_irq(&pi_state->owner->pi_lock);
|
|
WARN_ON(list_empty(&pi_state->list));
|
|
list_del_init(&pi_state->list);
|
|
spin_unlock_irq(&pi_state->owner->pi_lock);
|
|
|
|
spin_lock_irq(&new_owner->pi_lock);
|
|
WARN_ON(!list_empty(&pi_state->list));
|
|
list_add(&pi_state->list, &new_owner->pi_state_list);
|
|
pi_state->owner = new_owner;
|
|
spin_unlock_irq(&new_owner->pi_lock);
|
|
|
|
spin_unlock(&pi_state->pi_mutex.wait_lock);
|
|
rt_mutex_unlock(&pi_state->pi_mutex);
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int unlock_futex_pi(u32 __user *uaddr, u32 uval)
|
|
{
|
|
u32 oldval;
|
|
|
|
/*
|
|
* There is no waiter, so we unlock the futex. The owner died
|
|
* bit has not to be preserved here. We are the owner:
|
|
*/
|
|
oldval = cmpxchg_futex_value_locked(uaddr, uval, 0);
|
|
|
|
if (oldval == -EFAULT)
|
|
return oldval;
|
|
if (oldval != uval)
|
|
return -EAGAIN;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Express the locking dependencies for lockdep:
|
|
*/
|
|
static inline void
|
|
double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
|
{
|
|
if (hb1 <= hb2) {
|
|
spin_lock(&hb1->lock);
|
|
if (hb1 < hb2)
|
|
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
|
|
} else { /* hb1 > hb2 */
|
|
spin_lock(&hb2->lock);
|
|
spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
|
|
}
|
|
}
|
|
|
|
static inline void
|
|
double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
|
|
{
|
|
spin_unlock(&hb1->lock);
|
|
if (hb1 != hb2)
|
|
spin_unlock(&hb2->lock);
|
|
}
|
|
|
|
/*
|
|
* Wake up waiters matching bitset queued on this futex (uaddr).
|
|
*/
|
|
static int futex_wake(u32 __user *uaddr, int fshared, int nr_wake, u32 bitset)
|
|
{
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q *this, *next;
|
|
struct plist_head *head;
|
|
union futex_key key = FUTEX_KEY_INIT;
|
|
int ret;
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
|
|
ret = get_futex_key(uaddr, fshared, &key, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
hb = hash_futex(&key);
|
|
spin_lock(&hb->lock);
|
|
head = &hb->chain;
|
|
|
|
plist_for_each_entry_safe(this, next, head, list) {
|
|
if (match_futex (&this->key, &key)) {
|
|
if (this->pi_state || this->rt_waiter) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/* Check if one of the bits is set in both bitsets */
|
|
if (!(this->bitset & bitset))
|
|
continue;
|
|
|
|
wake_futex(this);
|
|
if (++ret >= nr_wake)
|
|
break;
|
|
}
|
|
}
|
|
|
|
spin_unlock(&hb->lock);
|
|
put_futex_key(fshared, &key);
|
|
out:
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Wake up all waiters hashed on the physical page that is mapped
|
|
* to this virtual address:
|
|
*/
|
|
static int
|
|
futex_wake_op(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
|
|
int nr_wake, int nr_wake2, int op)
|
|
{
|
|
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
|
struct futex_hash_bucket *hb1, *hb2;
|
|
struct plist_head *head;
|
|
struct futex_q *this, *next;
|
|
int ret, op_ret;
|
|
|
|
retry:
|
|
ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out_put_key1;
|
|
|
|
hb1 = hash_futex(&key1);
|
|
hb2 = hash_futex(&key2);
|
|
|
|
retry_private:
|
|
double_lock_hb(hb1, hb2);
|
|
op_ret = futex_atomic_op_inuser(op, uaddr2);
|
|
if (unlikely(op_ret < 0)) {
|
|
|
|
double_unlock_hb(hb1, hb2);
|
|
|
|
#ifndef CONFIG_MMU
|
|
/*
|
|
* we don't get EFAULT from MMU faults if we don't have an MMU,
|
|
* but we might get them from range checking
|
|
*/
|
|
ret = op_ret;
|
|
goto out_put_keys;
|
|
#endif
|
|
|
|
if (unlikely(op_ret != -EFAULT)) {
|
|
ret = op_ret;
|
|
goto out_put_keys;
|
|
}
|
|
|
|
ret = fault_in_user_writeable(uaddr2);
|
|
if (ret)
|
|
goto out_put_keys;
|
|
|
|
if (!fshared)
|
|
goto retry_private;
|
|
|
|
put_futex_key(fshared, &key2);
|
|
put_futex_key(fshared, &key1);
|
|
goto retry;
|
|
}
|
|
|
|
head = &hb1->chain;
|
|
|
|
plist_for_each_entry_safe(this, next, head, list) {
|
|
if (match_futex (&this->key, &key1)) {
|
|
wake_futex(this);
|
|
if (++ret >= nr_wake)
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (op_ret > 0) {
|
|
head = &hb2->chain;
|
|
|
|
op_ret = 0;
|
|
plist_for_each_entry_safe(this, next, head, list) {
|
|
if (match_futex (&this->key, &key2)) {
|
|
wake_futex(this);
|
|
if (++op_ret >= nr_wake2)
|
|
break;
|
|
}
|
|
}
|
|
ret += op_ret;
|
|
}
|
|
|
|
double_unlock_hb(hb1, hb2);
|
|
out_put_keys:
|
|
put_futex_key(fshared, &key2);
|
|
out_put_key1:
|
|
put_futex_key(fshared, &key1);
|
|
out:
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* requeue_futex() - Requeue a futex_q from one hb to another
|
|
* @q: the futex_q to requeue
|
|
* @hb1: the source hash_bucket
|
|
* @hb2: the target hash_bucket
|
|
* @key2: the new key for the requeued futex_q
|
|
*/
|
|
static inline
|
|
void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
|
|
struct futex_hash_bucket *hb2, union futex_key *key2)
|
|
{
|
|
|
|
/*
|
|
* If key1 and key2 hash to the same bucket, no need to
|
|
* requeue.
|
|
*/
|
|
if (likely(&hb1->chain != &hb2->chain)) {
|
|
plist_del(&q->list, &hb1->chain);
|
|
plist_add(&q->list, &hb2->chain);
|
|
q->lock_ptr = &hb2->lock;
|
|
#ifdef CONFIG_DEBUG_PI_LIST
|
|
q->list.plist.lock = &hb2->lock;
|
|
#endif
|
|
}
|
|
get_futex_key_refs(key2);
|
|
q->key = *key2;
|
|
}
|
|
|
|
/**
|
|
* requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
|
|
* @q: the futex_q
|
|
* @key: the key of the requeue target futex
|
|
* @hb: the hash_bucket of the requeue target futex
|
|
*
|
|
* During futex_requeue, with requeue_pi=1, it is possible to acquire the
|
|
* target futex if it is uncontended or via a lock steal. Set the futex_q key
|
|
* to the requeue target futex so the waiter can detect the wakeup on the right
|
|
* futex, but remove it from the hb and NULL the rt_waiter so it can detect
|
|
* atomic lock acquisition. Set the q->lock_ptr to the requeue target hb->lock
|
|
* to protect access to the pi_state to fixup the owner later. Must be called
|
|
* with both q->lock_ptr and hb->lock held.
|
|
*/
|
|
static inline
|
|
void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
|
|
struct futex_hash_bucket *hb)
|
|
{
|
|
get_futex_key_refs(key);
|
|
q->key = *key;
|
|
|
|
WARN_ON(plist_node_empty(&q->list));
|
|
plist_del(&q->list, &q->list.plist);
|
|
|
|
WARN_ON(!q->rt_waiter);
|
|
q->rt_waiter = NULL;
|
|
|
|
q->lock_ptr = &hb->lock;
|
|
#ifdef CONFIG_DEBUG_PI_LIST
|
|
q->list.plist.lock = &hb->lock;
|
|
#endif
|
|
|
|
wake_up_state(q->task, TASK_NORMAL);
|
|
}
|
|
|
|
/**
|
|
* futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
|
|
* @pifutex: the user address of the to futex
|
|
* @hb1: the from futex hash bucket, must be locked by the caller
|
|
* @hb2: the to futex hash bucket, must be locked by the caller
|
|
* @key1: the from futex key
|
|
* @key2: the to futex key
|
|
* @ps: address to store the pi_state pointer
|
|
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
|
|
*
|
|
* Try and get the lock on behalf of the top waiter if we can do it atomically.
|
|
* Wake the top waiter if we succeed. If the caller specified set_waiters,
|
|
* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
|
|
* hb1 and hb2 must be held by the caller.
|
|
*
|
|
* Returns:
|
|
* 0 - failed to acquire the lock atomicly
|
|
* 1 - acquired the lock
|
|
* <0 - error
|
|
*/
|
|
static int futex_proxy_trylock_atomic(u32 __user *pifutex,
|
|
struct futex_hash_bucket *hb1,
|
|
struct futex_hash_bucket *hb2,
|
|
union futex_key *key1, union futex_key *key2,
|
|
struct futex_pi_state **ps, int set_waiters)
|
|
{
|
|
struct futex_q *top_waiter = NULL;
|
|
u32 curval;
|
|
int ret;
|
|
|
|
if (get_futex_value_locked(&curval, pifutex))
|
|
return -EFAULT;
|
|
|
|
/*
|
|
* Find the top_waiter and determine if there are additional waiters.
|
|
* If the caller intends to requeue more than 1 waiter to pifutex,
|
|
* force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
|
|
* as we have means to handle the possible fault. If not, don't set
|
|
* the bit unecessarily as it will force the subsequent unlock to enter
|
|
* the kernel.
|
|
*/
|
|
top_waiter = futex_top_waiter(hb1, key1);
|
|
|
|
/* There are no waiters, nothing for us to do. */
|
|
if (!top_waiter)
|
|
return 0;
|
|
|
|
/* Ensure we requeue to the expected futex. */
|
|
if (!match_futex(top_waiter->requeue_pi_key, key2))
|
|
return -EINVAL;
|
|
|
|
/*
|
|
* Try to take the lock for top_waiter. Set the FUTEX_WAITERS bit in
|
|
* the contended case or if set_waiters is 1. The pi_state is returned
|
|
* in ps in contended cases.
|
|
*/
|
|
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
|
|
set_waiters);
|
|
if (ret == 1)
|
|
requeue_pi_wake_futex(top_waiter, key2, hb2);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* futex_requeue() - Requeue waiters from uaddr1 to uaddr2
|
|
* uaddr1: source futex user address
|
|
* uaddr2: target futex user address
|
|
* nr_wake: number of waiters to wake (must be 1 for requeue_pi)
|
|
* nr_requeue: number of waiters to requeue (0-INT_MAX)
|
|
* requeue_pi: if we are attempting to requeue from a non-pi futex to a
|
|
* pi futex (pi to pi requeue is not supported)
|
|
*
|
|
* Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
|
|
* uaddr2 atomically on behalf of the top waiter.
|
|
*
|
|
* Returns:
|
|
* >=0 - on success, the number of tasks requeued or woken
|
|
* <0 - on error
|
|
*/
|
|
static int futex_requeue(u32 __user *uaddr1, int fshared, u32 __user *uaddr2,
|
|
int nr_wake, int nr_requeue, u32 *cmpval,
|
|
int requeue_pi)
|
|
{
|
|
union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
|
|
int drop_count = 0, task_count = 0, ret;
|
|
struct futex_pi_state *pi_state = NULL;
|
|
struct futex_hash_bucket *hb1, *hb2;
|
|
struct plist_head *head1;
|
|
struct futex_q *this, *next;
|
|
u32 curval2;
|
|
|
|
if (requeue_pi) {
|
|
/*
|
|
* requeue_pi requires a pi_state, try to allocate it now
|
|
* without any locks in case it fails.
|
|
*/
|
|
if (refill_pi_state_cache())
|
|
return -ENOMEM;
|
|
/*
|
|
* requeue_pi must wake as many tasks as it can, up to nr_wake
|
|
* + nr_requeue, since it acquires the rt_mutex prior to
|
|
* returning to userspace, so as to not leave the rt_mutex with
|
|
* waiters and no owner. However, second and third wake-ups
|
|
* cannot be predicted as they involve race conditions with the
|
|
* first wake and a fault while looking up the pi_state. Both
|
|
* pthread_cond_signal() and pthread_cond_broadcast() should
|
|
* use nr_wake=1.
|
|
*/
|
|
if (nr_wake != 1)
|
|
return -EINVAL;
|
|
}
|
|
|
|
retry:
|
|
if (pi_state != NULL) {
|
|
/*
|
|
* We will have to lookup the pi_state again, so free this one
|
|
* to keep the accounting correct.
|
|
*/
|
|
free_pi_state(pi_state);
|
|
pi_state = NULL;
|
|
}
|
|
|
|
ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
ret = get_futex_key(uaddr2, fshared, &key2,
|
|
requeue_pi ? VERIFY_WRITE : VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
goto out_put_key1;
|
|
|
|
hb1 = hash_futex(&key1);
|
|
hb2 = hash_futex(&key2);
|
|
|
|
retry_private:
|
|
double_lock_hb(hb1, hb2);
|
|
|
|
if (likely(cmpval != NULL)) {
|
|
u32 curval;
|
|
|
|
ret = get_futex_value_locked(&curval, uaddr1);
|
|
|
|
if (unlikely(ret)) {
|
|
double_unlock_hb(hb1, hb2);
|
|
|
|
ret = get_user(curval, uaddr1);
|
|
if (ret)
|
|
goto out_put_keys;
|
|
|
|
if (!fshared)
|
|
goto retry_private;
|
|
|
|
put_futex_key(fshared, &key2);
|
|
put_futex_key(fshared, &key1);
|
|
goto retry;
|
|
}
|
|
if (curval != *cmpval) {
|
|
ret = -EAGAIN;
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
|
|
/*
|
|
* Attempt to acquire uaddr2 and wake the top waiter. If we
|
|
* intend to requeue waiters, force setting the FUTEX_WAITERS
|
|
* bit. We force this here where we are able to easily handle
|
|
* faults rather in the requeue loop below.
|
|
*/
|
|
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
|
|
&key2, &pi_state, nr_requeue);
|
|
|
|
/*
|
|
* At this point the top_waiter has either taken uaddr2 or is
|
|
* waiting on it. If the former, then the pi_state will not
|
|
* exist yet, look it up one more time to ensure we have a
|
|
* reference to it.
|
|
*/
|
|
if (ret == 1) {
|
|
WARN_ON(pi_state);
|
|
drop_count++;
|
|
task_count++;
|
|
ret = get_futex_value_locked(&curval2, uaddr2);
|
|
if (!ret)
|
|
ret = lookup_pi_state(curval2, hb2, &key2,
|
|
&pi_state);
|
|
}
|
|
|
|
switch (ret) {
|
|
case 0:
|
|
break;
|
|
case -EFAULT:
|
|
double_unlock_hb(hb1, hb2);
|
|
put_futex_key(fshared, &key2);
|
|
put_futex_key(fshared, &key1);
|
|
ret = fault_in_user_writeable(uaddr2);
|
|
if (!ret)
|
|
goto retry;
|
|
goto out;
|
|
case -EAGAIN:
|
|
/* The owner was exiting, try again. */
|
|
double_unlock_hb(hb1, hb2);
|
|
put_futex_key(fshared, &key2);
|
|
put_futex_key(fshared, &key1);
|
|
cond_resched();
|
|
goto retry;
|
|
default:
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
|
|
head1 = &hb1->chain;
|
|
plist_for_each_entry_safe(this, next, head1, list) {
|
|
if (task_count - nr_wake >= nr_requeue)
|
|
break;
|
|
|
|
if (!match_futex(&this->key, &key1))
|
|
continue;
|
|
|
|
/*
|
|
* FUTEX_WAIT_REQEUE_PI and FUTEX_CMP_REQUEUE_PI should always
|
|
* be paired with each other and no other futex ops.
|
|
*/
|
|
if ((requeue_pi && !this->rt_waiter) ||
|
|
(!requeue_pi && this->rt_waiter)) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Wake nr_wake waiters. For requeue_pi, if we acquired the
|
|
* lock, we already woke the top_waiter. If not, it will be
|
|
* woken by futex_unlock_pi().
|
|
*/
|
|
if (++task_count <= nr_wake && !requeue_pi) {
|
|
wake_futex(this);
|
|
continue;
|
|
}
|
|
|
|
/* Ensure we requeue to the expected futex for requeue_pi. */
|
|
if (requeue_pi && !match_futex(this->requeue_pi_key, &key2)) {
|
|
ret = -EINVAL;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Requeue nr_requeue waiters and possibly one more in the case
|
|
* of requeue_pi if we couldn't acquire the lock atomically.
|
|
*/
|
|
if (requeue_pi) {
|
|
/* Prepare the waiter to take the rt_mutex. */
|
|
atomic_inc(&pi_state->refcount);
|
|
this->pi_state = pi_state;
|
|
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
|
|
this->rt_waiter,
|
|
this->task, 1);
|
|
if (ret == 1) {
|
|
/* We got the lock. */
|
|
requeue_pi_wake_futex(this, &key2, hb2);
|
|
drop_count++;
|
|
continue;
|
|
} else if (ret) {
|
|
/* -EDEADLK */
|
|
this->pi_state = NULL;
|
|
free_pi_state(pi_state);
|
|
goto out_unlock;
|
|
}
|
|
}
|
|
requeue_futex(this, hb1, hb2, &key2);
|
|
drop_count++;
|
|
}
|
|
|
|
out_unlock:
|
|
double_unlock_hb(hb1, hb2);
|
|
|
|
/*
|
|
* drop_futex_key_refs() must be called outside the spinlocks. During
|
|
* the requeue we moved futex_q's from the hash bucket at key1 to the
|
|
* one at key2 and updated their key pointer. We no longer need to
|
|
* hold the references to key1.
|
|
*/
|
|
while (--drop_count >= 0)
|
|
drop_futex_key_refs(&key1);
|
|
|
|
out_put_keys:
|
|
put_futex_key(fshared, &key2);
|
|
out_put_key1:
|
|
put_futex_key(fshared, &key1);
|
|
out:
|
|
if (pi_state != NULL)
|
|
free_pi_state(pi_state);
|
|
return ret ? ret : task_count;
|
|
}
|
|
|
|
/* The key must be already stored in q->key. */
|
|
static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
|
|
{
|
|
struct futex_hash_bucket *hb;
|
|
|
|
get_futex_key_refs(&q->key);
|
|
hb = hash_futex(&q->key);
|
|
q->lock_ptr = &hb->lock;
|
|
|
|
spin_lock(&hb->lock);
|
|
return hb;
|
|
}
|
|
|
|
static inline void
|
|
queue_unlock(struct futex_q *q, struct futex_hash_bucket *hb)
|
|
{
|
|
spin_unlock(&hb->lock);
|
|
drop_futex_key_refs(&q->key);
|
|
}
|
|
|
|
/**
|
|
* queue_me() - Enqueue the futex_q on the futex_hash_bucket
|
|
* @q: The futex_q to enqueue
|
|
* @hb: The destination hash bucket
|
|
*
|
|
* The hb->lock must be held by the caller, and is released here. A call to
|
|
* queue_me() is typically paired with exactly one call to unqueue_me(). The
|
|
* exceptions involve the PI related operations, which may use unqueue_me_pi()
|
|
* or nothing if the unqueue is done as part of the wake process and the unqueue
|
|
* state is implicit in the state of woken task (see futex_wait_requeue_pi() for
|
|
* an example).
|
|
*/
|
|
static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
|
|
{
|
|
int prio;
|
|
|
|
/*
|
|
* The priority used to register this element is
|
|
* - either the real thread-priority for the real-time threads
|
|
* (i.e. threads with a priority lower than MAX_RT_PRIO)
|
|
* - or MAX_RT_PRIO for non-RT threads.
|
|
* Thus, all RT-threads are woken first in priority order, and
|
|
* the others are woken last, in FIFO order.
|
|
*/
|
|
prio = min(current->normal_prio, MAX_RT_PRIO);
|
|
|
|
plist_node_init(&q->list, prio);
|
|
#ifdef CONFIG_DEBUG_PI_LIST
|
|
q->list.plist.lock = &hb->lock;
|
|
#endif
|
|
plist_add(&q->list, &hb->chain);
|
|
q->task = current;
|
|
spin_unlock(&hb->lock);
|
|
}
|
|
|
|
/**
|
|
* unqueue_me() - Remove the futex_q from its futex_hash_bucket
|
|
* @q: The futex_q to unqueue
|
|
*
|
|
* The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
|
|
* be paired with exactly one earlier call to queue_me().
|
|
*
|
|
* Returns:
|
|
* 1 - if the futex_q was still queued (and we removed unqueued it)
|
|
* 0 - if the futex_q was already removed by the waking thread
|
|
*/
|
|
static int unqueue_me(struct futex_q *q)
|
|
{
|
|
spinlock_t *lock_ptr;
|
|
int ret = 0;
|
|
|
|
/* In the common case we don't take the spinlock, which is nice. */
|
|
retry:
|
|
lock_ptr = q->lock_ptr;
|
|
barrier();
|
|
if (lock_ptr != NULL) {
|
|
spin_lock(lock_ptr);
|
|
/*
|
|
* q->lock_ptr can change between reading it and
|
|
* spin_lock(), causing us to take the wrong lock. This
|
|
* corrects the race condition.
|
|
*
|
|
* Reasoning goes like this: if we have the wrong lock,
|
|
* q->lock_ptr must have changed (maybe several times)
|
|
* between reading it and the spin_lock(). It can
|
|
* change again after the spin_lock() but only if it was
|
|
* already changed before the spin_lock(). It cannot,
|
|
* however, change back to the original value. Therefore
|
|
* we can detect whether we acquired the correct lock.
|
|
*/
|
|
if (unlikely(lock_ptr != q->lock_ptr)) {
|
|
spin_unlock(lock_ptr);
|
|
goto retry;
|
|
}
|
|
WARN_ON(plist_node_empty(&q->list));
|
|
plist_del(&q->list, &q->list.plist);
|
|
|
|
BUG_ON(q->pi_state);
|
|
|
|
spin_unlock(lock_ptr);
|
|
ret = 1;
|
|
}
|
|
|
|
drop_futex_key_refs(&q->key);
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* PI futexes can not be requeued and must remove themself from the
|
|
* hash bucket. The hash bucket lock (i.e. lock_ptr) is held on entry
|
|
* and dropped here.
|
|
*/
|
|
static void unqueue_me_pi(struct futex_q *q)
|
|
{
|
|
WARN_ON(plist_node_empty(&q->list));
|
|
plist_del(&q->list, &q->list.plist);
|
|
|
|
BUG_ON(!q->pi_state);
|
|
free_pi_state(q->pi_state);
|
|
q->pi_state = NULL;
|
|
|
|
spin_unlock(q->lock_ptr);
|
|
|
|
drop_futex_key_refs(&q->key);
|
|
}
|
|
|
|
/*
|
|
* Fixup the pi_state owner with the new owner.
|
|
*
|
|
* Must be called with hash bucket lock held and mm->sem held for non
|
|
* private futexes.
|
|
*/
|
|
static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
|
|
struct task_struct *newowner, int fshared)
|
|
{
|
|
u32 newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
|
|
struct futex_pi_state *pi_state = q->pi_state;
|
|
struct task_struct *oldowner = pi_state->owner;
|
|
u32 uval, curval, newval;
|
|
int ret;
|
|
|
|
/* Owner died? */
|
|
if (!pi_state->owner)
|
|
newtid |= FUTEX_OWNER_DIED;
|
|
|
|
/*
|
|
* We are here either because we stole the rtmutex from the
|
|
* pending owner or we are the pending owner which failed to
|
|
* get the rtmutex. We have to replace the pending owner TID
|
|
* in the user space variable. This must be atomic as we have
|
|
* to preserve the owner died bit here.
|
|
*
|
|
* Note: We write the user space value _before_ changing the pi_state
|
|
* because we can fault here. Imagine swapped out pages or a fork
|
|
* that marked all the anonymous memory readonly for cow.
|
|
*
|
|
* Modifying pi_state _before_ the user space value would
|
|
* leave the pi_state in an inconsistent state when we fault
|
|
* here, because we need to drop the hash bucket lock to
|
|
* handle the fault. This might be observed in the PID check
|
|
* in lookup_pi_state.
|
|
*/
|
|
retry:
|
|
if (get_futex_value_locked(&uval, uaddr))
|
|
goto handle_fault;
|
|
|
|
while (1) {
|
|
newval = (uval & FUTEX_OWNER_DIED) | newtid;
|
|
|
|
curval = cmpxchg_futex_value_locked(uaddr, uval, newval);
|
|
|
|
if (curval == -EFAULT)
|
|
goto handle_fault;
|
|
if (curval == uval)
|
|
break;
|
|
uval = curval;
|
|
}
|
|
|
|
/*
|
|
* We fixed up user space. Now we need to fix the pi_state
|
|
* itself.
|
|
*/
|
|
if (pi_state->owner != NULL) {
|
|
spin_lock_irq(&pi_state->owner->pi_lock);
|
|
WARN_ON(list_empty(&pi_state->list));
|
|
list_del_init(&pi_state->list);
|
|
spin_unlock_irq(&pi_state->owner->pi_lock);
|
|
}
|
|
|
|
pi_state->owner = newowner;
|
|
|
|
spin_lock_irq(&newowner->pi_lock);
|
|
WARN_ON(!list_empty(&pi_state->list));
|
|
list_add(&pi_state->list, &newowner->pi_state_list);
|
|
spin_unlock_irq(&newowner->pi_lock);
|
|
return 0;
|
|
|
|
/*
|
|
* To handle the page fault we need to drop the hash bucket
|
|
* lock here. That gives the other task (either the pending
|
|
* owner itself or the task which stole the rtmutex) the
|
|
* chance to try the fixup of the pi_state. So once we are
|
|
* back from handling the fault we need to check the pi_state
|
|
* after reacquiring the hash bucket lock and before trying to
|
|
* do another fixup. When the fixup has been done already we
|
|
* simply return.
|
|
*/
|
|
handle_fault:
|
|
spin_unlock(q->lock_ptr);
|
|
|
|
ret = fault_in_user_writeable(uaddr);
|
|
|
|
spin_lock(q->lock_ptr);
|
|
|
|
/*
|
|
* Check if someone else fixed it for us:
|
|
*/
|
|
if (pi_state->owner != oldowner)
|
|
return 0;
|
|
|
|
if (ret)
|
|
return ret;
|
|
|
|
goto retry;
|
|
}
|
|
|
|
/*
|
|
* In case we must use restart_block to restart a futex_wait,
|
|
* we encode in the 'flags' shared capability
|
|
*/
|
|
#define FLAGS_SHARED 0x01
|
|
#define FLAGS_CLOCKRT 0x02
|
|
#define FLAGS_HAS_TIMEOUT 0x04
|
|
|
|
static long futex_wait_restart(struct restart_block *restart);
|
|
|
|
/**
|
|
* fixup_owner() - Post lock pi_state and corner case management
|
|
* @uaddr: user address of the futex
|
|
* @fshared: whether the futex is shared (1) or not (0)
|
|
* @q: futex_q (contains pi_state and access to the rt_mutex)
|
|
* @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
|
|
*
|
|
* After attempting to lock an rt_mutex, this function is called to cleanup
|
|
* the pi_state owner as well as handle race conditions that may allow us to
|
|
* acquire the lock. Must be called with the hb lock held.
|
|
*
|
|
* Returns:
|
|
* 1 - success, lock taken
|
|
* 0 - success, lock not taken
|
|
* <0 - on error (-EFAULT)
|
|
*/
|
|
static int fixup_owner(u32 __user *uaddr, int fshared, struct futex_q *q,
|
|
int locked)
|
|
{
|
|
struct task_struct *owner;
|
|
int ret = 0;
|
|
|
|
if (locked) {
|
|
/*
|
|
* Got the lock. We might not be the anticipated owner if we
|
|
* did a lock-steal - fix up the PI-state in that case:
|
|
*/
|
|
if (q->pi_state->owner != current)
|
|
ret = fixup_pi_state_owner(uaddr, q, current, fshared);
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* Catch the rare case, where the lock was released when we were on the
|
|
* way back before we locked the hash bucket.
|
|
*/
|
|
if (q->pi_state->owner == current) {
|
|
/*
|
|
* Try to get the rt_mutex now. This might fail as some other
|
|
* task acquired the rt_mutex after we removed ourself from the
|
|
* rt_mutex waiters list.
|
|
*/
|
|
if (rt_mutex_trylock(&q->pi_state->pi_mutex)) {
|
|
locked = 1;
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* pi_state is incorrect, some other task did a lock steal and
|
|
* we returned due to timeout or signal without taking the
|
|
* rt_mutex. Too late. We can access the rt_mutex_owner without
|
|
* locking, as the other task is now blocked on the hash bucket
|
|
* lock. Fix the state up.
|
|
*/
|
|
owner = rt_mutex_owner(&q->pi_state->pi_mutex);
|
|
ret = fixup_pi_state_owner(uaddr, q, owner, fshared);
|
|
goto out;
|
|
}
|
|
|
|
/*
|
|
* Paranoia check. If we did not take the lock, then we should not be
|
|
* the owner, nor the pending owner, of the rt_mutex.
|
|
*/
|
|
if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
|
|
printk(KERN_ERR "fixup_owner: ret = %d pi-mutex: %p "
|
|
"pi-state %p\n", ret,
|
|
q->pi_state->pi_mutex.owner,
|
|
q->pi_state->owner);
|
|
|
|
out:
|
|
return ret ? ret : locked;
|
|
}
|
|
|
|
/**
|
|
* futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
|
|
* @hb: the futex hash bucket, must be locked by the caller
|
|
* @q: the futex_q to queue up on
|
|
* @timeout: the prepared hrtimer_sleeper, or null for no timeout
|
|
*/
|
|
static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
|
|
struct hrtimer_sleeper *timeout)
|
|
{
|
|
/*
|
|
* The task state is guaranteed to be set before another task can
|
|
* wake it. set_current_state() is implemented using set_mb() and
|
|
* queue_me() calls spin_unlock() upon completion, both serializing
|
|
* access to the hash list and forcing another memory barrier.
|
|
*/
|
|
set_current_state(TASK_INTERRUPTIBLE);
|
|
queue_me(q, hb);
|
|
|
|
/* Arm the timer */
|
|
if (timeout) {
|
|
hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
|
|
if (!hrtimer_active(&timeout->timer))
|
|
timeout->task = NULL;
|
|
}
|
|
|
|
/*
|
|
* If we have been removed from the hash list, then another task
|
|
* has tried to wake us, and we can skip the call to schedule().
|
|
*/
|
|
if (likely(!plist_node_empty(&q->list))) {
|
|
/*
|
|
* If the timer has already expired, current will already be
|
|
* flagged for rescheduling. Only call schedule if there
|
|
* is no timeout, or if it has yet to expire.
|
|
*/
|
|
if (!timeout || timeout->task)
|
|
schedule();
|
|
}
|
|
__set_current_state(TASK_RUNNING);
|
|
}
|
|
|
|
/**
|
|
* futex_wait_setup() - Prepare to wait on a futex
|
|
* @uaddr: the futex userspace address
|
|
* @val: the expected value
|
|
* @fshared: whether the futex is shared (1) or not (0)
|
|
* @q: the associated futex_q
|
|
* @hb: storage for hash_bucket pointer to be returned to caller
|
|
*
|
|
* Setup the futex_q and locate the hash_bucket. Get the futex value and
|
|
* compare it with the expected value. Handle atomic faults internally.
|
|
* Return with the hb lock held and a q.key reference on success, and unlocked
|
|
* with no q.key reference on failure.
|
|
*
|
|
* Returns:
|
|
* 0 - uaddr contains val and hb has been locked
|
|
* <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlcoked
|
|
*/
|
|
static int futex_wait_setup(u32 __user *uaddr, u32 val, int fshared,
|
|
struct futex_q *q, struct futex_hash_bucket **hb)
|
|
{
|
|
u32 uval;
|
|
int ret;
|
|
|
|
/*
|
|
* Access the page AFTER the hash-bucket is locked.
|
|
* Order is important:
|
|
*
|
|
* Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
|
|
* Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
|
|
*
|
|
* The basic logical guarantee of a futex is that it blocks ONLY
|
|
* if cond(var) is known to be true at the time of blocking, for
|
|
* any cond. If we queued after testing *uaddr, that would open
|
|
* a race condition where we could block indefinitely with
|
|
* cond(var) false, which would violate the guarantee.
|
|
*
|
|
* A consequence is that futex_wait() can return zero and absorb
|
|
* a wakeup when *uaddr != val on entry to the syscall. This is
|
|
* rare, but normal.
|
|
*/
|
|
retry:
|
|
q->key = FUTEX_KEY_INIT;
|
|
ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ);
|
|
if (unlikely(ret != 0))
|
|
return ret;
|
|
|
|
retry_private:
|
|
*hb = queue_lock(q);
|
|
|
|
ret = get_futex_value_locked(&uval, uaddr);
|
|
|
|
if (ret) {
|
|
queue_unlock(q, *hb);
|
|
|
|
ret = get_user(uval, uaddr);
|
|
if (ret)
|
|
goto out;
|
|
|
|
if (!fshared)
|
|
goto retry_private;
|
|
|
|
put_futex_key(fshared, &q->key);
|
|
goto retry;
|
|
}
|
|
|
|
if (uval != val) {
|
|
queue_unlock(q, *hb);
|
|
ret = -EWOULDBLOCK;
|
|
}
|
|
|
|
out:
|
|
if (ret)
|
|
put_futex_key(fshared, &q->key);
|
|
return ret;
|
|
}
|
|
|
|
static int futex_wait(u32 __user *uaddr, int fshared,
|
|
u32 val, ktime_t *abs_time, u32 bitset, int clockrt)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to = NULL;
|
|
struct restart_block *restart;
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q q;
|
|
int ret;
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
|
|
q.pi_state = NULL;
|
|
q.bitset = bitset;
|
|
q.rt_waiter = NULL;
|
|
q.requeue_pi_key = NULL;
|
|
|
|
if (abs_time) {
|
|
to = &timeout;
|
|
|
|
hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
|
|
CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
|
|
hrtimer_init_sleeper(to, current);
|
|
hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
|
current->timer_slack_ns);
|
|
}
|
|
|
|
retry:
|
|
/* Prepare to wait on uaddr. */
|
|
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
|
|
if (ret)
|
|
goto out;
|
|
|
|
/* queue_me and wait for wakeup, timeout, or a signal. */
|
|
futex_wait_queue_me(hb, &q, to);
|
|
|
|
/* If we were woken (and unqueued), we succeeded, whatever. */
|
|
ret = 0;
|
|
if (!unqueue_me(&q))
|
|
goto out_put_key;
|
|
ret = -ETIMEDOUT;
|
|
if (to && !to->task)
|
|
goto out_put_key;
|
|
|
|
/*
|
|
* We expect signal_pending(current), but we might be the
|
|
* victim of a spurious wakeup as well.
|
|
*/
|
|
if (!signal_pending(current)) {
|
|
put_futex_key(fshared, &q.key);
|
|
goto retry;
|
|
}
|
|
|
|
ret = -ERESTARTSYS;
|
|
if (!abs_time)
|
|
goto out_put_key;
|
|
|
|
restart = ¤t_thread_info()->restart_block;
|
|
restart->fn = futex_wait_restart;
|
|
restart->futex.uaddr = (u32 *)uaddr;
|
|
restart->futex.val = val;
|
|
restart->futex.time = abs_time->tv64;
|
|
restart->futex.bitset = bitset;
|
|
restart->futex.flags = FLAGS_HAS_TIMEOUT;
|
|
|
|
if (fshared)
|
|
restart->futex.flags |= FLAGS_SHARED;
|
|
if (clockrt)
|
|
restart->futex.flags |= FLAGS_CLOCKRT;
|
|
|
|
ret = -ERESTART_RESTARTBLOCK;
|
|
|
|
out_put_key:
|
|
put_futex_key(fshared, &q.key);
|
|
out:
|
|
if (to) {
|
|
hrtimer_cancel(&to->timer);
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
|
|
static long futex_wait_restart(struct restart_block *restart)
|
|
{
|
|
u32 __user *uaddr = (u32 __user *)restart->futex.uaddr;
|
|
int fshared = 0;
|
|
ktime_t t, *tp = NULL;
|
|
|
|
if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
|
|
t.tv64 = restart->futex.time;
|
|
tp = &t;
|
|
}
|
|
restart->fn = do_no_restart_syscall;
|
|
if (restart->futex.flags & FLAGS_SHARED)
|
|
fshared = 1;
|
|
return (long)futex_wait(uaddr, fshared, restart->futex.val, tp,
|
|
restart->futex.bitset,
|
|
restart->futex.flags & FLAGS_CLOCKRT);
|
|
}
|
|
|
|
|
|
/*
|
|
* Userspace tried a 0 -> TID atomic transition of the futex value
|
|
* and failed. The kernel side here does the whole locking operation:
|
|
* if there are waiters then it will block, it does PI, etc. (Due to
|
|
* races the kernel might see a 0 value of the futex too.)
|
|
*/
|
|
static int futex_lock_pi(u32 __user *uaddr, int fshared,
|
|
int detect, ktime_t *time, int trylock)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to = NULL;
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q q;
|
|
int res, ret;
|
|
|
|
if (refill_pi_state_cache())
|
|
return -ENOMEM;
|
|
|
|
if (time) {
|
|
to = &timeout;
|
|
hrtimer_init_on_stack(&to->timer, CLOCK_REALTIME,
|
|
HRTIMER_MODE_ABS);
|
|
hrtimer_init_sleeper(to, current);
|
|
hrtimer_set_expires(&to->timer, *time);
|
|
}
|
|
|
|
q.pi_state = NULL;
|
|
q.rt_waiter = NULL;
|
|
q.requeue_pi_key = NULL;
|
|
retry:
|
|
q.key = FUTEX_KEY_INIT;
|
|
ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
retry_private:
|
|
hb = queue_lock(&q);
|
|
|
|
ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
|
|
if (unlikely(ret)) {
|
|
switch (ret) {
|
|
case 1:
|
|
/* We got the lock. */
|
|
ret = 0;
|
|
goto out_unlock_put_key;
|
|
case -EFAULT:
|
|
goto uaddr_faulted;
|
|
case -EAGAIN:
|
|
/*
|
|
* Task is exiting and we just wait for the
|
|
* exit to complete.
|
|
*/
|
|
queue_unlock(&q, hb);
|
|
put_futex_key(fshared, &q.key);
|
|
cond_resched();
|
|
goto retry;
|
|
default:
|
|
goto out_unlock_put_key;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Only actually queue now that the atomic ops are done:
|
|
*/
|
|
queue_me(&q, hb);
|
|
|
|
WARN_ON(!q.pi_state);
|
|
/*
|
|
* Block on the PI mutex:
|
|
*/
|
|
if (!trylock)
|
|
ret = rt_mutex_timed_lock(&q.pi_state->pi_mutex, to, 1);
|
|
else {
|
|
ret = rt_mutex_trylock(&q.pi_state->pi_mutex);
|
|
/* Fixup the trylock return value: */
|
|
ret = ret ? 0 : -EWOULDBLOCK;
|
|
}
|
|
|
|
spin_lock(q.lock_ptr);
|
|
/*
|
|
* Fixup the pi_state owner and possibly acquire the lock if we
|
|
* haven't already.
|
|
*/
|
|
res = fixup_owner(uaddr, fshared, &q, !ret);
|
|
/*
|
|
* If fixup_owner() returned an error, proprogate that. If it acquired
|
|
* the lock, clear our -ETIMEDOUT or -EINTR.
|
|
*/
|
|
if (res)
|
|
ret = (res < 0) ? res : 0;
|
|
|
|
/*
|
|
* If fixup_owner() faulted and was unable to handle the fault, unlock
|
|
* it and return the fault to userspace.
|
|
*/
|
|
if (ret && (rt_mutex_owner(&q.pi_state->pi_mutex) == current))
|
|
rt_mutex_unlock(&q.pi_state->pi_mutex);
|
|
|
|
/* Unqueue and drop the lock */
|
|
unqueue_me_pi(&q);
|
|
|
|
goto out;
|
|
|
|
out_unlock_put_key:
|
|
queue_unlock(&q, hb);
|
|
|
|
out_put_key:
|
|
put_futex_key(fshared, &q.key);
|
|
out:
|
|
if (to)
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
return ret != -EINTR ? ret : -ERESTARTNOINTR;
|
|
|
|
uaddr_faulted:
|
|
queue_unlock(&q, hb);
|
|
|
|
ret = fault_in_user_writeable(uaddr);
|
|
if (ret)
|
|
goto out_put_key;
|
|
|
|
if (!fshared)
|
|
goto retry_private;
|
|
|
|
put_futex_key(fshared, &q.key);
|
|
goto retry;
|
|
}
|
|
|
|
/*
|
|
* Userspace attempted a TID -> 0 atomic transition, and failed.
|
|
* This is the in-kernel slowpath: we look up the PI state (if any),
|
|
* and do the rt-mutex unlock.
|
|
*/
|
|
static int futex_unlock_pi(u32 __user *uaddr, int fshared)
|
|
{
|
|
struct futex_hash_bucket *hb;
|
|
struct futex_q *this, *next;
|
|
u32 uval;
|
|
struct plist_head *head;
|
|
union futex_key key = FUTEX_KEY_INIT;
|
|
int ret;
|
|
|
|
retry:
|
|
if (get_user(uval, uaddr))
|
|
return -EFAULT;
|
|
/*
|
|
* We release only a lock we actually own:
|
|
*/
|
|
if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current))
|
|
return -EPERM;
|
|
|
|
ret = get_futex_key(uaddr, fshared, &key, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
hb = hash_futex(&key);
|
|
spin_lock(&hb->lock);
|
|
|
|
/*
|
|
* To avoid races, try to do the TID -> 0 atomic transition
|
|
* again. If it succeeds then we can return without waking
|
|
* anyone else up:
|
|
*/
|
|
if (!(uval & FUTEX_OWNER_DIED))
|
|
uval = cmpxchg_futex_value_locked(uaddr, task_pid_vnr(current), 0);
|
|
|
|
|
|
if (unlikely(uval == -EFAULT))
|
|
goto pi_faulted;
|
|
/*
|
|
* Rare case: we managed to release the lock atomically,
|
|
* no need to wake anyone else up:
|
|
*/
|
|
if (unlikely(uval == task_pid_vnr(current)))
|
|
goto out_unlock;
|
|
|
|
/*
|
|
* Ok, other tasks may need to be woken up - check waiters
|
|
* and do the wakeup if necessary:
|
|
*/
|
|
head = &hb->chain;
|
|
|
|
plist_for_each_entry_safe(this, next, head, list) {
|
|
if (!match_futex (&this->key, &key))
|
|
continue;
|
|
ret = wake_futex_pi(uaddr, uval, this);
|
|
/*
|
|
* The atomic access to the futex value
|
|
* generated a pagefault, so retry the
|
|
* user-access and the wakeup:
|
|
*/
|
|
if (ret == -EFAULT)
|
|
goto pi_faulted;
|
|
goto out_unlock;
|
|
}
|
|
/*
|
|
* No waiters - kernel unlocks the futex:
|
|
*/
|
|
if (!(uval & FUTEX_OWNER_DIED)) {
|
|
ret = unlock_futex_pi(uaddr, uval);
|
|
if (ret == -EFAULT)
|
|
goto pi_faulted;
|
|
}
|
|
|
|
out_unlock:
|
|
spin_unlock(&hb->lock);
|
|
put_futex_key(fshared, &key);
|
|
|
|
out:
|
|
return ret;
|
|
|
|
pi_faulted:
|
|
spin_unlock(&hb->lock);
|
|
put_futex_key(fshared, &key);
|
|
|
|
ret = fault_in_user_writeable(uaddr);
|
|
if (!ret)
|
|
goto retry;
|
|
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* handle_early_requeue_pi_wakeup() - Detect early wakeup on the initial futex
|
|
* @hb: the hash_bucket futex_q was original enqueued on
|
|
* @q: the futex_q woken while waiting to be requeued
|
|
* @key2: the futex_key of the requeue target futex
|
|
* @timeout: the timeout associated with the wait (NULL if none)
|
|
*
|
|
* Detect if the task was woken on the initial futex as opposed to the requeue
|
|
* target futex. If so, determine if it was a timeout or a signal that caused
|
|
* the wakeup and return the appropriate error code to the caller. Must be
|
|
* called with the hb lock held.
|
|
*
|
|
* Returns
|
|
* 0 - no early wakeup detected
|
|
* <0 - -ETIMEDOUT or -ERESTARTNOINTR
|
|
*/
|
|
static inline
|
|
int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
|
|
struct futex_q *q, union futex_key *key2,
|
|
struct hrtimer_sleeper *timeout)
|
|
{
|
|
int ret = 0;
|
|
|
|
/*
|
|
* With the hb lock held, we avoid races while we process the wakeup.
|
|
* We only need to hold hb (and not hb2) to ensure atomicity as the
|
|
* wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
|
|
* It can't be requeued from uaddr2 to something else since we don't
|
|
* support a PI aware source futex for requeue.
|
|
*/
|
|
if (!match_futex(&q->key, key2)) {
|
|
WARN_ON(q->lock_ptr && (&hb->lock != q->lock_ptr));
|
|
/*
|
|
* We were woken prior to requeue by a timeout or a signal.
|
|
* Unqueue the futex_q and determine which it was.
|
|
*/
|
|
plist_del(&q->list, &q->list.plist);
|
|
|
|
/* Handle spurious wakeups gracefully */
|
|
ret = -EAGAIN;
|
|
if (timeout && !timeout->task)
|
|
ret = -ETIMEDOUT;
|
|
else if (signal_pending(current))
|
|
ret = -ERESTARTNOINTR;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/**
|
|
* futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
|
|
* @uaddr: the futex we initially wait on (non-pi)
|
|
* @fshared: whether the futexes are shared (1) or not (0). They must be
|
|
* the same type, no requeueing from private to shared, etc.
|
|
* @val: the expected value of uaddr
|
|
* @abs_time: absolute timeout
|
|
* @bitset: 32 bit wakeup bitset set by userspace, defaults to all
|
|
* @clockrt: whether to use CLOCK_REALTIME (1) or CLOCK_MONOTONIC (0)
|
|
* @uaddr2: the pi futex we will take prior to returning to user-space
|
|
*
|
|
* The caller will wait on uaddr and will be requeued by futex_requeue() to
|
|
* uaddr2 which must be PI aware. Normal wakeup will wake on uaddr2 and
|
|
* complete the acquisition of the rt_mutex prior to returning to userspace.
|
|
* This ensures the rt_mutex maintains an owner when it has waiters; without
|
|
* one, the pi logic wouldn't know which task to boost/deboost, if there was a
|
|
* need to.
|
|
*
|
|
* We call schedule in futex_wait_queue_me() when we enqueue and return there
|
|
* via the following:
|
|
* 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
|
|
* 2) wakeup on uaddr2 after a requeue
|
|
* 3) signal
|
|
* 4) timeout
|
|
*
|
|
* If 3, cleanup and return -ERESTARTNOINTR.
|
|
*
|
|
* If 2, we may then block on trying to take the rt_mutex and return via:
|
|
* 5) successful lock
|
|
* 6) signal
|
|
* 7) timeout
|
|
* 8) other lock acquisition failure
|
|
*
|
|
* If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
|
|
*
|
|
* If 4 or 7, we cleanup and return with -ETIMEDOUT.
|
|
*
|
|
* Returns:
|
|
* 0 - On success
|
|
* <0 - On error
|
|
*/
|
|
static int futex_wait_requeue_pi(u32 __user *uaddr, int fshared,
|
|
u32 val, ktime_t *abs_time, u32 bitset,
|
|
int clockrt, u32 __user *uaddr2)
|
|
{
|
|
struct hrtimer_sleeper timeout, *to = NULL;
|
|
struct rt_mutex_waiter rt_waiter;
|
|
struct rt_mutex *pi_mutex = NULL;
|
|
struct futex_hash_bucket *hb;
|
|
union futex_key key2;
|
|
struct futex_q q;
|
|
int res, ret;
|
|
|
|
if (!bitset)
|
|
return -EINVAL;
|
|
|
|
if (abs_time) {
|
|
to = &timeout;
|
|
hrtimer_init_on_stack(&to->timer, clockrt ? CLOCK_REALTIME :
|
|
CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
|
|
hrtimer_init_sleeper(to, current);
|
|
hrtimer_set_expires_range_ns(&to->timer, *abs_time,
|
|
current->timer_slack_ns);
|
|
}
|
|
|
|
/*
|
|
* The waiter is allocated on our stack, manipulated by the requeue
|
|
* code while we sleep on uaddr.
|
|
*/
|
|
debug_rt_mutex_init_waiter(&rt_waiter);
|
|
rt_waiter.task = NULL;
|
|
|
|
retry:
|
|
key2 = FUTEX_KEY_INIT;
|
|
ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE);
|
|
if (unlikely(ret != 0))
|
|
goto out;
|
|
|
|
q.pi_state = NULL;
|
|
q.bitset = bitset;
|
|
q.rt_waiter = &rt_waiter;
|
|
q.requeue_pi_key = &key2;
|
|
|
|
/* Prepare to wait on uaddr. */
|
|
ret = futex_wait_setup(uaddr, val, fshared, &q, &hb);
|
|
if (ret)
|
|
goto out_key2;
|
|
|
|
/* Queue the futex_q, drop the hb lock, wait for wakeup. */
|
|
futex_wait_queue_me(hb, &q, to);
|
|
|
|
spin_lock(&hb->lock);
|
|
ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
|
|
spin_unlock(&hb->lock);
|
|
if (ret)
|
|
goto out_put_keys;
|
|
|
|
/*
|
|
* In order for us to be here, we know our q.key == key2, and since
|
|
* we took the hb->lock above, we also know that futex_requeue() has
|
|
* completed and we no longer have to concern ourselves with a wakeup
|
|
* race with the atomic proxy lock acquition by the requeue code.
|
|
*/
|
|
|
|
/* Check if the requeue code acquired the second futex for us. */
|
|
if (!q.rt_waiter) {
|
|
/*
|
|
* Got the lock. We might not be the anticipated owner if we
|
|
* did a lock-steal - fix up the PI-state in that case.
|
|
*/
|
|
if (q.pi_state && (q.pi_state->owner != current)) {
|
|
spin_lock(q.lock_ptr);
|
|
ret = fixup_pi_state_owner(uaddr2, &q, current,
|
|
fshared);
|
|
spin_unlock(q.lock_ptr);
|
|
}
|
|
} else {
|
|
/*
|
|
* We have been woken up by futex_unlock_pi(), a timeout, or a
|
|
* signal. futex_unlock_pi() will not destroy the lock_ptr nor
|
|
* the pi_state.
|
|
*/
|
|
WARN_ON(!&q.pi_state);
|
|
pi_mutex = &q.pi_state->pi_mutex;
|
|
ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
|
|
debug_rt_mutex_free_waiter(&rt_waiter);
|
|
|
|
spin_lock(q.lock_ptr);
|
|
/*
|
|
* Fixup the pi_state owner and possibly acquire the lock if we
|
|
* haven't already.
|
|
*/
|
|
res = fixup_owner(uaddr2, fshared, &q, !ret);
|
|
/*
|
|
* If fixup_owner() returned an error, proprogate that. If it
|
|
* acquired the lock, clear -ETIMEDOUT or -EINTR.
|
|
*/
|
|
if (res)
|
|
ret = (res < 0) ? res : 0;
|
|
|
|
/* Unqueue and drop the lock. */
|
|
unqueue_me_pi(&q);
|
|
}
|
|
|
|
/*
|
|
* If fixup_pi_state_owner() faulted and was unable to handle the
|
|
* fault, unlock the rt_mutex and return the fault to userspace.
|
|
*/
|
|
if (ret == -EFAULT) {
|
|
if (rt_mutex_owner(pi_mutex) == current)
|
|
rt_mutex_unlock(pi_mutex);
|
|
} else if (ret == -EINTR) {
|
|
/*
|
|
* We've already been requeued, but cannot restart by calling
|
|
* futex_lock_pi() directly. We could restart this syscall, but
|
|
* it would detect that the user space "val" changed and return
|
|
* -EWOULDBLOCK. Save the overhead of the restart and return
|
|
* -EWOULDBLOCK directly.
|
|
*/
|
|
ret = -EWOULDBLOCK;
|
|
}
|
|
|
|
out_put_keys:
|
|
put_futex_key(fshared, &q.key);
|
|
out_key2:
|
|
put_futex_key(fshared, &key2);
|
|
|
|
/* Spurious wakeup ? */
|
|
if (ret == -EAGAIN)
|
|
goto retry;
|
|
out:
|
|
if (to) {
|
|
hrtimer_cancel(&to->timer);
|
|
destroy_hrtimer_on_stack(&to->timer);
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Support for robust futexes: the kernel cleans up held futexes at
|
|
* thread exit time.
|
|
*
|
|
* Implementation: user-space maintains a per-thread list of locks it
|
|
* is holding. Upon do_exit(), the kernel carefully walks this list,
|
|
* and marks all locks that are owned by this thread with the
|
|
* FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
|
|
* always manipulated with the lock held, so the list is private and
|
|
* per-thread. Userspace also maintains a per-thread 'list_op_pending'
|
|
* field, to allow the kernel to clean up if the thread dies after
|
|
* acquiring the lock, but just before it could have added itself to
|
|
* the list. There can only be one such pending lock.
|
|
*/
|
|
|
|
/**
|
|
* sys_set_robust_list() - Set the robust-futex list head of a task
|
|
* @head: pointer to the list-head
|
|
* @len: length of the list-head, as userspace expects
|
|
*/
|
|
SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
|
|
size_t, len)
|
|
{
|
|
if (!futex_cmpxchg_enabled)
|
|
return -ENOSYS;
|
|
/*
|
|
* The kernel knows only one size for now:
|
|
*/
|
|
if (unlikely(len != sizeof(*head)))
|
|
return -EINVAL;
|
|
|
|
current->robust_list = head;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/**
|
|
* sys_get_robust_list() - Get the robust-futex list head of a task
|
|
* @pid: pid of the process [zero for current task]
|
|
* @head_ptr: pointer to a list-head pointer, the kernel fills it in
|
|
* @len_ptr: pointer to a length field, the kernel fills in the header size
|
|
*/
|
|
SYSCALL_DEFINE3(get_robust_list, int, pid,
|
|
struct robust_list_head __user * __user *, head_ptr,
|
|
size_t __user *, len_ptr)
|
|
{
|
|
struct robust_list_head __user *head;
|
|
unsigned long ret;
|
|
const struct cred *cred = current_cred(), *pcred;
|
|
|
|
if (!futex_cmpxchg_enabled)
|
|
return -ENOSYS;
|
|
|
|
if (!pid)
|
|
head = current->robust_list;
|
|
else {
|
|
struct task_struct *p;
|
|
|
|
ret = -ESRCH;
|
|
rcu_read_lock();
|
|
p = find_task_by_vpid(pid);
|
|
if (!p)
|
|
goto err_unlock;
|
|
ret = -EPERM;
|
|
pcred = __task_cred(p);
|
|
if (cred->euid != pcred->euid &&
|
|
cred->euid != pcred->uid &&
|
|
!capable(CAP_SYS_PTRACE))
|
|
goto err_unlock;
|
|
head = p->robust_list;
|
|
rcu_read_unlock();
|
|
}
|
|
|
|
if (put_user(sizeof(*head), len_ptr))
|
|
return -EFAULT;
|
|
return put_user(head, head_ptr);
|
|
|
|
err_unlock:
|
|
rcu_read_unlock();
|
|
|
|
return ret;
|
|
}
|
|
|
|
/*
|
|
* Process a futex-list entry, check whether it's owned by the
|
|
* dying task, and do notification if so:
|
|
*/
|
|
int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
|
|
{
|
|
u32 uval, nval, mval;
|
|
|
|
retry:
|
|
if (get_user(uval, uaddr))
|
|
return -1;
|
|
|
|
if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) {
|
|
/*
|
|
* Ok, this dying thread is truly holding a futex
|
|
* of interest. Set the OWNER_DIED bit atomically
|
|
* via cmpxchg, and if the value had FUTEX_WAITERS
|
|
* set, wake up a waiter (if any). (We have to do a
|
|
* futex_wake() even if OWNER_DIED is already set -
|
|
* to handle the rare but possible case of recursive
|
|
* thread-death.) The rest of the cleanup is done in
|
|
* userspace.
|
|
*/
|
|
mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
|
|
nval = futex_atomic_cmpxchg_inatomic(uaddr, uval, mval);
|
|
|
|
if (nval == -EFAULT)
|
|
return -1;
|
|
|
|
if (nval != uval)
|
|
goto retry;
|
|
|
|
/*
|
|
* Wake robust non-PI futexes here. The wakeup of
|
|
* PI futexes happens in exit_pi_state():
|
|
*/
|
|
if (!pi && (uval & FUTEX_WAITERS))
|
|
futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Fetch a robust-list pointer. Bit 0 signals PI futexes:
|
|
*/
|
|
static inline int fetch_robust_entry(struct robust_list __user **entry,
|
|
struct robust_list __user * __user *head,
|
|
int *pi)
|
|
{
|
|
unsigned long uentry;
|
|
|
|
if (get_user(uentry, (unsigned long __user *)head))
|
|
return -EFAULT;
|
|
|
|
*entry = (void __user *)(uentry & ~1UL);
|
|
*pi = uentry & 1;
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Walk curr->robust_list (very carefully, it's a userspace list!)
|
|
* and mark any locks found there dead, and notify any waiters.
|
|
*
|
|
* We silently return on any sign of list-walking problem.
|
|
*/
|
|
void exit_robust_list(struct task_struct *curr)
|
|
{
|
|
struct robust_list_head __user *head = curr->robust_list;
|
|
struct robust_list __user *entry, *next_entry, *pending;
|
|
unsigned int limit = ROBUST_LIST_LIMIT, pi, next_pi, pip;
|
|
unsigned long futex_offset;
|
|
int rc;
|
|
|
|
if (!futex_cmpxchg_enabled)
|
|
return;
|
|
|
|
/*
|
|
* Fetch the list head (which was registered earlier, via
|
|
* sys_set_robust_list()):
|
|
*/
|
|
if (fetch_robust_entry(&entry, &head->list.next, &pi))
|
|
return;
|
|
/*
|
|
* Fetch the relative futex offset:
|
|
*/
|
|
if (get_user(futex_offset, &head->futex_offset))
|
|
return;
|
|
/*
|
|
* Fetch any possibly pending lock-add first, and handle it
|
|
* if it exists:
|
|
*/
|
|
if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
|
|
return;
|
|
|
|
next_entry = NULL; /* avoid warning with gcc */
|
|
while (entry != &head->list) {
|
|
/*
|
|
* Fetch the next entry in the list before calling
|
|
* handle_futex_death:
|
|
*/
|
|
rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
|
|
/*
|
|
* A pending lock might already be on the list, so
|
|
* don't process it twice:
|
|
*/
|
|
if (entry != pending)
|
|
if (handle_futex_death((void __user *)entry + futex_offset,
|
|
curr, pi))
|
|
return;
|
|
if (rc)
|
|
return;
|
|
entry = next_entry;
|
|
pi = next_pi;
|
|
/*
|
|
* Avoid excessively long or circular lists:
|
|
*/
|
|
if (!--limit)
|
|
break;
|
|
|
|
cond_resched();
|
|
}
|
|
|
|
if (pending)
|
|
handle_futex_death((void __user *)pending + futex_offset,
|
|
curr, pip);
|
|
}
|
|
|
|
long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
|
|
u32 __user *uaddr2, u32 val2, u32 val3)
|
|
{
|
|
int clockrt, ret = -ENOSYS;
|
|
int cmd = op & FUTEX_CMD_MASK;
|
|
int fshared = 0;
|
|
|
|
if (!(op & FUTEX_PRIVATE_FLAG))
|
|
fshared = 1;
|
|
|
|
clockrt = op & FUTEX_CLOCK_REALTIME;
|
|
if (clockrt && cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI)
|
|
return -ENOSYS;
|
|
|
|
switch (cmd) {
|
|
case FUTEX_WAIT:
|
|
val3 = FUTEX_BITSET_MATCH_ANY;
|
|
case FUTEX_WAIT_BITSET:
|
|
ret = futex_wait(uaddr, fshared, val, timeout, val3, clockrt);
|
|
break;
|
|
case FUTEX_WAKE:
|
|
val3 = FUTEX_BITSET_MATCH_ANY;
|
|
case FUTEX_WAKE_BITSET:
|
|
ret = futex_wake(uaddr, fshared, val, val3);
|
|
break;
|
|
case FUTEX_REQUEUE:
|
|
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, NULL, 0);
|
|
break;
|
|
case FUTEX_CMP_REQUEUE:
|
|
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
|
|
0);
|
|
break;
|
|
case FUTEX_WAKE_OP:
|
|
ret = futex_wake_op(uaddr, fshared, uaddr2, val, val2, val3);
|
|
break;
|
|
case FUTEX_LOCK_PI:
|
|
if (futex_cmpxchg_enabled)
|
|
ret = futex_lock_pi(uaddr, fshared, val, timeout, 0);
|
|
break;
|
|
case FUTEX_UNLOCK_PI:
|
|
if (futex_cmpxchg_enabled)
|
|
ret = futex_unlock_pi(uaddr, fshared);
|
|
break;
|
|
case FUTEX_TRYLOCK_PI:
|
|
if (futex_cmpxchg_enabled)
|
|
ret = futex_lock_pi(uaddr, fshared, 0, timeout, 1);
|
|
break;
|
|
case FUTEX_WAIT_REQUEUE_PI:
|
|
val3 = FUTEX_BITSET_MATCH_ANY;
|
|
ret = futex_wait_requeue_pi(uaddr, fshared, val, timeout, val3,
|
|
clockrt, uaddr2);
|
|
break;
|
|
case FUTEX_CMP_REQUEUE_PI:
|
|
ret = futex_requeue(uaddr, fshared, uaddr2, val, val2, &val3,
|
|
1);
|
|
break;
|
|
default:
|
|
ret = -ENOSYS;
|
|
}
|
|
return ret;
|
|
}
|
|
|
|
|
|
SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
|
|
struct timespec __user *, utime, u32 __user *, uaddr2,
|
|
u32, val3)
|
|
{
|
|
struct timespec ts;
|
|
ktime_t t, *tp = NULL;
|
|
u32 val2 = 0;
|
|
int cmd = op & FUTEX_CMD_MASK;
|
|
|
|
if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
|
|
cmd == FUTEX_WAIT_BITSET ||
|
|
cmd == FUTEX_WAIT_REQUEUE_PI)) {
|
|
if (copy_from_user(&ts, utime, sizeof(ts)) != 0)
|
|
return -EFAULT;
|
|
if (!timespec_valid(&ts))
|
|
return -EINVAL;
|
|
|
|
t = timespec_to_ktime(ts);
|
|
if (cmd == FUTEX_WAIT)
|
|
t = ktime_add_safe(ktime_get(), t);
|
|
tp = &t;
|
|
}
|
|
/*
|
|
* requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*.
|
|
* number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP.
|
|
*/
|
|
if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
|
|
cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP)
|
|
val2 = (u32) (unsigned long) utime;
|
|
|
|
return do_futex(uaddr, op, val, tp, uaddr2, val2, val3);
|
|
}
|
|
|
|
static int __init futex_init(void)
|
|
{
|
|
u32 curval;
|
|
int i;
|
|
|
|
/*
|
|
* This will fail and we want it. Some arch implementations do
|
|
* runtime detection of the futex_atomic_cmpxchg_inatomic()
|
|
* functionality. We want to know that before we call in any
|
|
* of the complex code paths. Also we want to prevent
|
|
* registration of robust lists in that case. NULL is
|
|
* guaranteed to fault and we get -EFAULT on functional
|
|
* implementation, the non functional ones will return
|
|
* -ENOSYS.
|
|
*/
|
|
curval = cmpxchg_futex_value_locked(NULL, 0, 0);
|
|
if (curval == -EFAULT)
|
|
futex_cmpxchg_enabled = 1;
|
|
|
|
for (i = 0; i < ARRAY_SIZE(futex_queues); i++) {
|
|
plist_head_init(&futex_queues[i].chain, &futex_queues[i].lock);
|
|
spin_lock_init(&futex_queues[i].lock);
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
__initcall(futex_init);
|