![Ross Zwisler](/assets/img/avatar_default.png)
There are four cases I can see where we could end up with a NULL 'slot' in
radix_tree_next_slot(). Yet radix_tree_next_slot() never actually checks
whether 'slot' is NULL. It just happens that for the cases where 'slot'
is NULL, some other combination of factors prevents us from dereferencing
it.
It would be very easy for someone to unwittingly change one of these
factors without realizing that we are implicitly depending on it to save
us from a NULL pointer dereference.
Add a comment documenting the things that allow 'slot' to be safely passed
as NULL to radix_tree_next_slot().
Here are details on the four cases:
1) radix_tree_iter_retry() via a non-tagged iteration like
radix_tree_for_each_slot(). In this case we currently aren't seeing a bug
because radix_tree_iter_retry() sets
iter->next_index = iter->index;
which means that in in the else case in radix_tree_next_slot(), 'count' is
zero, so we skip over the while() loop and effectively just return NULL
without ever dereferencing 'slot'.
2) radix_tree_iter_retry() via tagged iteration like
radix_tree_for_each_tagged(). This case was giving us NULL pointer
dereferences in testing, and was fixed with this commit:
commit 3cb9185c67
("radix-tree: fix radix_tree_iter_retry() for tagged
iterators.")
This fix doesn't explicitly check for 'slot' being NULL, though, it works
around the NULL pointer dereference by instead zeroing iter->tags in
radix_tree_iter_retry(), which makes us bail out of the if() case in
radix_tree_next_slot() before we dereference 'slot'.
3) radix_tree_iter_next() via via a non-tagged iteration like
radix_tree_for_each_slot(). This currently happens in shmem_tag_pins()
and shmem_partial_swap_usage().
As with non-tagged iteration, 'count' in the else case of
radix_tree_next_slot() is zero, so we skip over the while() loop and
effectively just return NULL without ever dereferencing 'slot'.
4) radix_tree_iter_next() via tagged iteration like
radix_tree_for_each_tagged(). This happens in shmem_wait_for_pins().
radix_tree_iter_next() zeros out iter->tags, so we end up exiting
radix_tree_next_slot() here:
if (flags & RADIX_TREE_ITER_TAGGED) {
void *canon = slot;
iter->tags >>= 1;
if (unlikely(!iter->tags))
return NULL;
Link: http://lkml.kernel.org/r/20160815194237.25967-2-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
583 lines
20 KiB
C
583 lines
20 KiB
C
/*
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* Copyright (C) 2001 Momchil Velikov
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* Portions Copyright (C) 2001 Christoph Hellwig
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* Copyright (C) 2006 Nick Piggin
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* Copyright (C) 2012 Konstantin Khlebnikov
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2, or (at
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* 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, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* 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., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#ifndef _LINUX_RADIX_TREE_H
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#define _LINUX_RADIX_TREE_H
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#include <linux/bitops.h>
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#include <linux/preempt.h>
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#include <linux/types.h>
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#include <linux/bug.h>
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#include <linux/kernel.h>
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#include <linux/rcupdate.h>
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/*
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* The bottom two bits of the slot determine how the remaining bits in the
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* slot are interpreted:
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*
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* 00 - data pointer
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* 01 - internal entry
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* 10 - exceptional entry
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* 11 - this bit combination is currently unused/reserved
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*
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* The internal entry may be a pointer to the next level in the tree, a
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* sibling entry, or an indicator that the entry in this slot has been moved
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* to another location in the tree and the lookup should be restarted. While
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* NULL fits the 'data pointer' pattern, it means that there is no entry in
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* the tree for this index (no matter what level of the tree it is found at).
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* This means that you cannot store NULL in the tree as a value for the index.
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*/
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#define RADIX_TREE_ENTRY_MASK 3UL
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#define RADIX_TREE_INTERNAL_NODE 1UL
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/*
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* Most users of the radix tree store pointers but shmem/tmpfs stores swap
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* entries in the same tree. They are marked as exceptional entries to
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* distinguish them from pointers to struct page.
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* EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it.
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*/
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#define RADIX_TREE_EXCEPTIONAL_ENTRY 2
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#define RADIX_TREE_EXCEPTIONAL_SHIFT 2
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static inline bool radix_tree_is_internal_node(void *ptr)
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{
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return ((unsigned long)ptr & RADIX_TREE_ENTRY_MASK) ==
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RADIX_TREE_INTERNAL_NODE;
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}
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/*** radix-tree API starts here ***/
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#define RADIX_TREE_MAX_TAGS 3
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#ifndef RADIX_TREE_MAP_SHIFT
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#define RADIX_TREE_MAP_SHIFT (CONFIG_BASE_SMALL ? 4 : 6)
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#endif
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#define RADIX_TREE_MAP_SIZE (1UL << RADIX_TREE_MAP_SHIFT)
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#define RADIX_TREE_MAP_MASK (RADIX_TREE_MAP_SIZE-1)
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#define RADIX_TREE_TAG_LONGS \
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((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG)
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#define RADIX_TREE_INDEX_BITS (8 /* CHAR_BIT */ * sizeof(unsigned long))
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#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
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RADIX_TREE_MAP_SHIFT))
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/* Internally used bits of node->count */
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#define RADIX_TREE_COUNT_SHIFT (RADIX_TREE_MAP_SHIFT + 1)
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#define RADIX_TREE_COUNT_MASK ((1UL << RADIX_TREE_COUNT_SHIFT) - 1)
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struct radix_tree_node {
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unsigned char shift; /* Bits remaining in each slot */
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unsigned char offset; /* Slot offset in parent */
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unsigned int count;
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union {
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struct {
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/* Used when ascending tree */
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struct radix_tree_node *parent;
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/* For tree user */
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void *private_data;
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};
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/* Used when freeing node */
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struct rcu_head rcu_head;
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};
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/* For tree user */
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struct list_head private_list;
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void __rcu *slots[RADIX_TREE_MAP_SIZE];
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unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS];
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};
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/* root tags are stored in gfp_mask, shifted by __GFP_BITS_SHIFT */
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struct radix_tree_root {
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gfp_t gfp_mask;
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struct radix_tree_node __rcu *rnode;
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};
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#define RADIX_TREE_INIT(mask) { \
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.gfp_mask = (mask), \
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.rnode = NULL, \
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}
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#define RADIX_TREE(name, mask) \
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struct radix_tree_root name = RADIX_TREE_INIT(mask)
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#define INIT_RADIX_TREE(root, mask) \
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do { \
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(root)->gfp_mask = (mask); \
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(root)->rnode = NULL; \
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} while (0)
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static inline bool radix_tree_empty(struct radix_tree_root *root)
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{
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return root->rnode == NULL;
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}
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/**
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* Radix-tree synchronization
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*
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* The radix-tree API requires that users provide all synchronisation (with
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* specific exceptions, noted below).
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*
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* Synchronization of access to the data items being stored in the tree, and
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* management of their lifetimes must be completely managed by API users.
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*
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* For API usage, in general,
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* - any function _modifying_ the tree or tags (inserting or deleting
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* items, setting or clearing tags) must exclude other modifications, and
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* exclude any functions reading the tree.
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* - any function _reading_ the tree or tags (looking up items or tags,
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* gang lookups) must exclude modifications to the tree, but may occur
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* concurrently with other readers.
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*
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* The notable exceptions to this rule are the following functions:
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* __radix_tree_lookup
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* radix_tree_lookup
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* radix_tree_lookup_slot
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* radix_tree_tag_get
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* radix_tree_gang_lookup
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* radix_tree_gang_lookup_slot
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* radix_tree_gang_lookup_tag
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* radix_tree_gang_lookup_tag_slot
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* radix_tree_tagged
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*
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* The first 8 functions are able to be called locklessly, using RCU. The
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* caller must ensure calls to these functions are made within rcu_read_lock()
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* regions. Other readers (lock-free or otherwise) and modifications may be
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* running concurrently.
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*
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* It is still required that the caller manage the synchronization and lifetimes
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* of the items. So if RCU lock-free lookups are used, typically this would mean
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* that the items have their own locks, or are amenable to lock-free access; and
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* that the items are freed by RCU (or only freed after having been deleted from
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* the radix tree *and* a synchronize_rcu() grace period).
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*
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* (Note, rcu_assign_pointer and rcu_dereference are not needed to control
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* access to data items when inserting into or looking up from the radix tree)
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*
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* Note that the value returned by radix_tree_tag_get() may not be relied upon
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* if only the RCU read lock is held. Functions to set/clear tags and to
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* delete nodes running concurrently with it may affect its result such that
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* two consecutive reads in the same locked section may return different
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* values. If reliability is required, modification functions must also be
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* excluded from concurrency.
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*
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* radix_tree_tagged is able to be called without locking or RCU.
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*/
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/**
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* radix_tree_deref_slot - dereference a slot
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* @pslot: pointer to slot, returned by radix_tree_lookup_slot
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* Returns: item that was stored in that slot with any direct pointer flag
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* removed.
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*
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* For use with radix_tree_lookup_slot(). Caller must hold tree at least read
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* locked across slot lookup and dereference. Not required if write lock is
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* held (ie. items cannot be concurrently inserted).
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*
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* radix_tree_deref_retry must be used to confirm validity of the pointer if
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* only the read lock is held.
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*/
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static inline void *radix_tree_deref_slot(void **pslot)
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{
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return rcu_dereference(*pslot);
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}
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/**
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* radix_tree_deref_slot_protected - dereference a slot without RCU lock but with tree lock held
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* @pslot: pointer to slot, returned by radix_tree_lookup_slot
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* Returns: item that was stored in that slot with any direct pointer flag
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* removed.
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*
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* Similar to radix_tree_deref_slot but only used during migration when a pages
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* mapping is being moved. The caller does not hold the RCU read lock but it
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* must hold the tree lock to prevent parallel updates.
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*/
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static inline void *radix_tree_deref_slot_protected(void **pslot,
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spinlock_t *treelock)
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{
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return rcu_dereference_protected(*pslot, lockdep_is_held(treelock));
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}
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/**
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* radix_tree_deref_retry - check radix_tree_deref_slot
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* @arg: pointer returned by radix_tree_deref_slot
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* Returns: 0 if retry is not required, otherwise retry is required
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*
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* radix_tree_deref_retry must be used with radix_tree_deref_slot.
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*/
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static inline int radix_tree_deref_retry(void *arg)
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{
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return unlikely(radix_tree_is_internal_node(arg));
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}
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/**
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* radix_tree_exceptional_entry - radix_tree_deref_slot gave exceptional entry?
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* @arg: value returned by radix_tree_deref_slot
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* Returns: 0 if well-aligned pointer, non-0 if exceptional entry.
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*/
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static inline int radix_tree_exceptional_entry(void *arg)
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{
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/* Not unlikely because radix_tree_exception often tested first */
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return (unsigned long)arg & RADIX_TREE_EXCEPTIONAL_ENTRY;
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}
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/**
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* radix_tree_exception - radix_tree_deref_slot returned either exception?
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* @arg: value returned by radix_tree_deref_slot
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* Returns: 0 if well-aligned pointer, non-0 if either kind of exception.
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*/
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static inline int radix_tree_exception(void *arg)
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{
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return unlikely((unsigned long)arg & RADIX_TREE_ENTRY_MASK);
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}
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/**
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* radix_tree_replace_slot - replace item in a slot
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* @pslot: pointer to slot, returned by radix_tree_lookup_slot
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* @item: new item to store in the slot.
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*
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* For use with radix_tree_lookup_slot(). Caller must hold tree write locked
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* across slot lookup and replacement.
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*/
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static inline void radix_tree_replace_slot(void **pslot, void *item)
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{
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BUG_ON(radix_tree_is_internal_node(item));
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rcu_assign_pointer(*pslot, item);
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}
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int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
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unsigned order, struct radix_tree_node **nodep,
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void ***slotp);
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int __radix_tree_insert(struct radix_tree_root *, unsigned long index,
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unsigned order, void *);
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static inline int radix_tree_insert(struct radix_tree_root *root,
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unsigned long index, void *entry)
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{
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return __radix_tree_insert(root, index, 0, entry);
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}
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void *__radix_tree_lookup(struct radix_tree_root *root, unsigned long index,
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struct radix_tree_node **nodep, void ***slotp);
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void *radix_tree_lookup(struct radix_tree_root *, unsigned long);
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void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long);
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bool __radix_tree_delete_node(struct radix_tree_root *root,
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struct radix_tree_node *node);
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void *radix_tree_delete_item(struct radix_tree_root *, unsigned long, void *);
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void *radix_tree_delete(struct radix_tree_root *, unsigned long);
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void radix_tree_clear_tags(struct radix_tree_root *root,
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struct radix_tree_node *node,
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void **slot);
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unsigned int radix_tree_gang_lookup(struct radix_tree_root *root,
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void **results, unsigned long first_index,
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unsigned int max_items);
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unsigned int radix_tree_gang_lookup_slot(struct radix_tree_root *root,
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void ***results, unsigned long *indices,
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unsigned long first_index, unsigned int max_items);
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int radix_tree_preload(gfp_t gfp_mask);
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int radix_tree_maybe_preload(gfp_t gfp_mask);
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int radix_tree_maybe_preload_order(gfp_t gfp_mask, int order);
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void radix_tree_init(void);
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void *radix_tree_tag_set(struct radix_tree_root *root,
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unsigned long index, unsigned int tag);
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void *radix_tree_tag_clear(struct radix_tree_root *root,
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unsigned long index, unsigned int tag);
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int radix_tree_tag_get(struct radix_tree_root *root,
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unsigned long index, unsigned int tag);
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unsigned int
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radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
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unsigned long first_index, unsigned int max_items,
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unsigned int tag);
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unsigned int
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radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
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unsigned long first_index, unsigned int max_items,
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unsigned int tag);
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unsigned long radix_tree_range_tag_if_tagged(struct radix_tree_root *root,
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unsigned long *first_indexp, unsigned long last_index,
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unsigned long nr_to_tag,
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unsigned int fromtag, unsigned int totag);
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int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);
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unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item);
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static inline void radix_tree_preload_end(void)
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{
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preempt_enable();
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}
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/**
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* struct radix_tree_iter - radix tree iterator state
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*
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* @index: index of current slot
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* @next_index: one beyond the last index for this chunk
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* @tags: bit-mask for tag-iterating
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* @shift: shift for the node that holds our slots
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*
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* This radix tree iterator works in terms of "chunks" of slots. A chunk is a
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* subinterval of slots contained within one radix tree leaf node. It is
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* described by a pointer to its first slot and a struct radix_tree_iter
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* which holds the chunk's position in the tree and its size. For tagged
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* iteration radix_tree_iter also holds the slots' bit-mask for one chosen
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* radix tree tag.
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*/
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struct radix_tree_iter {
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unsigned long index;
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unsigned long next_index;
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unsigned long tags;
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#ifdef CONFIG_RADIX_TREE_MULTIORDER
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unsigned int shift;
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#endif
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};
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static inline unsigned int iter_shift(struct radix_tree_iter *iter)
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{
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#ifdef CONFIG_RADIX_TREE_MULTIORDER
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return iter->shift;
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#else
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return 0;
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#endif
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}
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#define RADIX_TREE_ITER_TAG_MASK 0x00FF /* tag index in lower byte */
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#define RADIX_TREE_ITER_TAGGED 0x0100 /* lookup tagged slots */
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#define RADIX_TREE_ITER_CONTIG 0x0200 /* stop at first hole */
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/**
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* radix_tree_iter_init - initialize radix tree iterator
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*
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* @iter: pointer to iterator state
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* @start: iteration starting index
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* Returns: NULL
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*/
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static __always_inline void **
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radix_tree_iter_init(struct radix_tree_iter *iter, unsigned long start)
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{
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/*
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* Leave iter->tags uninitialized. radix_tree_next_chunk() will fill it
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* in the case of a successful tagged chunk lookup. If the lookup was
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* unsuccessful or non-tagged then nobody cares about ->tags.
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*
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* Set index to zero to bypass next_index overflow protection.
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* See the comment in radix_tree_next_chunk() for details.
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*/
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iter->index = 0;
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iter->next_index = start;
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return NULL;
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}
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/**
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* radix_tree_next_chunk - find next chunk of slots for iteration
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*
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* @root: radix tree root
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* @iter: iterator state
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* @flags: RADIX_TREE_ITER_* flags and tag index
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* Returns: pointer to chunk first slot, or NULL if there no more left
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*
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* This function looks up the next chunk in the radix tree starting from
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* @iter->next_index. It returns a pointer to the chunk's first slot.
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* Also it fills @iter with data about chunk: position in the tree (index),
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* its end (next_index), and constructs a bit mask for tagged iterating (tags).
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*/
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void **radix_tree_next_chunk(struct radix_tree_root *root,
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struct radix_tree_iter *iter, unsigned flags);
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/**
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* radix_tree_iter_retry - retry this chunk of the iteration
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* @iter: iterator state
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*
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* If we iterate over a tree protected only by the RCU lock, a race
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* against deletion or creation may result in seeing a slot for which
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* radix_tree_deref_retry() returns true. If so, call this function
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* and continue the iteration.
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*/
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static inline __must_check
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void **radix_tree_iter_retry(struct radix_tree_iter *iter)
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{
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iter->next_index = iter->index;
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iter->tags = 0;
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return NULL;
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}
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static inline unsigned long
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__radix_tree_iter_add(struct radix_tree_iter *iter, unsigned long slots)
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{
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return iter->index + (slots << iter_shift(iter));
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}
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/**
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* radix_tree_iter_next - resume iterating when the chunk may be invalid
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* @iter: iterator state
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*
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* If the iterator needs to release then reacquire a lock, the chunk may
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* have been invalidated by an insertion or deletion. Call this function
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* to continue the iteration from the next index.
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*/
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static inline __must_check
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void **radix_tree_iter_next(struct radix_tree_iter *iter)
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{
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iter->next_index = __radix_tree_iter_add(iter, 1);
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iter->tags = 0;
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return NULL;
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}
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/**
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* radix_tree_chunk_size - get current chunk size
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*
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* @iter: pointer to radix tree iterator
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* Returns: current chunk size
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*/
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static __always_inline long
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radix_tree_chunk_size(struct radix_tree_iter *iter)
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{
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return (iter->next_index - iter->index) >> iter_shift(iter);
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}
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static inline struct radix_tree_node *entry_to_node(void *ptr)
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{
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return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
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}
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/**
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* radix_tree_next_slot - find next slot in chunk
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*
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* @slot: pointer to current slot
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* @iter: pointer to interator state
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* @flags: RADIX_TREE_ITER_*, should be constant
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* Returns: pointer to next slot, or NULL if there no more left
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*
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* This function updates @iter->index in the case of a successful lookup.
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* For tagged lookup it also eats @iter->tags.
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*
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* There are several cases where 'slot' can be passed in as NULL to this
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* function. These cases result from the use of radix_tree_iter_next() or
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* radix_tree_iter_retry(). In these cases we don't end up dereferencing
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* 'slot' because either:
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* a) we are doing tagged iteration and iter->tags has been set to 0, or
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* b) we are doing non-tagged iteration, and iter->index and iter->next_index
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* have been set up so that radix_tree_chunk_size() returns 1 or 0.
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*/
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static __always_inline void **
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radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
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{
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if (flags & RADIX_TREE_ITER_TAGGED) {
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void *canon = slot;
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iter->tags >>= 1;
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if (unlikely(!iter->tags))
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return NULL;
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while (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
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radix_tree_is_internal_node(slot[1])) {
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if (entry_to_node(slot[1]) == canon) {
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iter->tags >>= 1;
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iter->index = __radix_tree_iter_add(iter, 1);
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slot++;
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continue;
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|
}
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iter->next_index = __radix_tree_iter_add(iter, 1);
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return NULL;
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|
}
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if (likely(iter->tags & 1ul)) {
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iter->index = __radix_tree_iter_add(iter, 1);
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return slot + 1;
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|
}
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if (!(flags & RADIX_TREE_ITER_CONTIG)) {
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unsigned offset = __ffs(iter->tags);
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|
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|
iter->tags >>= offset;
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iter->index = __radix_tree_iter_add(iter, offset + 1);
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return slot + offset + 1;
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|
}
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} else {
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|
long count = radix_tree_chunk_size(iter);
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|
void *canon = slot;
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|
|
|
while (--count > 0) {
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|
slot++;
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|
iter->index = __radix_tree_iter_add(iter, 1);
|
|
|
|
if (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
|
|
radix_tree_is_internal_node(*slot)) {
|
|
if (entry_to_node(*slot) == canon)
|
|
continue;
|
|
iter->next_index = iter->index;
|
|
break;
|
|
}
|
|
|
|
if (likely(*slot))
|
|
return slot;
|
|
if (flags & RADIX_TREE_ITER_CONTIG) {
|
|
/* forbid switching to the next chunk */
|
|
iter->next_index = 0;
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
/**
|
|
* radix_tree_for_each_slot - iterate over non-empty slots
|
|
*
|
|
* @slot: the void** variable for pointer to slot
|
|
* @root: the struct radix_tree_root pointer
|
|
* @iter: the struct radix_tree_iter pointer
|
|
* @start: iteration starting index
|
|
*
|
|
* @slot points to radix tree slot, @iter->index contains its index.
|
|
*/
|
|
#define radix_tree_for_each_slot(slot, root, iter, start) \
|
|
for (slot = radix_tree_iter_init(iter, start) ; \
|
|
slot || (slot = radix_tree_next_chunk(root, iter, 0)) ; \
|
|
slot = radix_tree_next_slot(slot, iter, 0))
|
|
|
|
/**
|
|
* radix_tree_for_each_contig - iterate over contiguous slots
|
|
*
|
|
* @slot: the void** variable for pointer to slot
|
|
* @root: the struct radix_tree_root pointer
|
|
* @iter: the struct radix_tree_iter pointer
|
|
* @start: iteration starting index
|
|
*
|
|
* @slot points to radix tree slot, @iter->index contains its index.
|
|
*/
|
|
#define radix_tree_for_each_contig(slot, root, iter, start) \
|
|
for (slot = radix_tree_iter_init(iter, start) ; \
|
|
slot || (slot = radix_tree_next_chunk(root, iter, \
|
|
RADIX_TREE_ITER_CONTIG)) ; \
|
|
slot = radix_tree_next_slot(slot, iter, \
|
|
RADIX_TREE_ITER_CONTIG))
|
|
|
|
/**
|
|
* radix_tree_for_each_tagged - iterate over tagged slots
|
|
*
|
|
* @slot: the void** variable for pointer to slot
|
|
* @root: the struct radix_tree_root pointer
|
|
* @iter: the struct radix_tree_iter pointer
|
|
* @start: iteration starting index
|
|
* @tag: tag index
|
|
*
|
|
* @slot points to radix tree slot, @iter->index contains its index.
|
|
*/
|
|
#define radix_tree_for_each_tagged(slot, root, iter, start, tag) \
|
|
for (slot = radix_tree_iter_init(iter, start) ; \
|
|
slot || (slot = radix_tree_next_chunk(root, iter, \
|
|
RADIX_TREE_ITER_TAGGED | tag)) ; \
|
|
slot = radix_tree_next_slot(slot, iter, \
|
|
RADIX_TREE_ITER_TAGGED))
|
|
|
|
#endif /* _LINUX_RADIX_TREE_H */
|