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Hugh Dickins a12f3ad8d9 shmem: fix possible deadlocks on shmlock_user_lock 
[ Upstream commit ea0dfeb420 ]

Recent commit 71725ed10c ("mm: huge tmpfs: try to split_huge_page()
when punching hole") has allowed syzkaller to probe deeper, uncovering a
long-standing lockdep issue between the irq-unsafe shmlock_user_lock,
the irq-safe xa_lock on mapping->i_pages, and shmem inode's info->lock
which nests inside xa_lock (or tree_lock) since 4.8's shmem_uncharge().

user_shm_lock(), servicing SysV shmctl(SHM_LOCK), wants
shmlock_user_lock while its caller shmem_lock() holds info->lock with
interrupts disabled; but hugetlbfs_file_setup() calls user_shm_lock()
with interrupts enabled, and might be interrupted by a writeback endio
wanting xa_lock on i_pages.

This may not risk an actual deadlock, since shmem inodes do not take
part in writeback accounting, but there are several easy ways to avoid
it.

Requiring interrupts disabled for shmlock_user_lock would be easy, but
it's a high-level global lock for which that seems inappropriate.
Instead, recall that the use of info->lock to guard info->flags in
shmem_lock() dates from pre-3.1 days, when races with SHMEM_PAGEIN and
SHMEM_TRUNCATE could occur: nowadays it serves no purpose, the only flag
added or removed is VM_LOCKED itself, and calls to shmem_lock() an inode
are already serialized by the caller.

Take info->lock out of the chain and the possibility of deadlock or
lockdep warning goes away.

Fixes: 4595ef88d1 ("shmem: make shmem_inode_info::lock irq-safe")
Reported-by: syzbot+c8a8197c8852f566b9d9@syzkaller.appspotmail.com
Reported-by: syzbot+40b71e145e73f78f81ad@syzkaller.appspotmail.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2004161707410.16322@eggly.anvils
Link: https://lore.kernel.org/lkml/000000000000e5838c05a3152f53@google.com/
Link: https://lore.kernel.org/lkml/0000000000003712b305a331d3b1@google.com/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2020-05-20 08:20:03 +02:00
Documentation USB: hub: Revert commit bd0e6c9614 ("usb: hub: try old enumeration scheme first for high speed devices") 2020-04-29 16:33:14 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch arch/x86/kvm/svm/sev.c: change flag passed to GUP fast in sev_pin_memory() 2020-05-14 07:58:29 +02:00
block iocost: protect iocg->abs_vdebt with iocg->waitq.lock 2020-05-14 07:58:27 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: rng - Fix a refcounting bug in crypto_rng_reset() 2020-04-17 10:50:16 +02:00
drivers iommu/virtio: Reverse arguments to list_add 2020-05-14 07:58:29 +02:00
fs fanotify: merge duplicate events on parent and child 2020-05-14 07:58:30 +02:00
include fsnotify: replace inode pointer with an object id 2020-05-14 07:58:30 +02:00
init printk: queue wake_up_klogd irq_work only if per-CPU areas are ready 2020-05-02 08:48:42 +02:00
ipc ipc/mqueue.c: change __do_notify() to bypass check_kill_permission() 2020-05-14 07:58:26 +02:00
kernel coredump: fix crash when umh is disabled 2020-05-14 07:58:27 +02:00
lib lib: devres: add a helper function for ioremap_uc 2020-05-10 10:31:30 +02:00
mm shmem: fix possible deadlocks on shmlock_user_lock 2020-05-20 08:20:03 +02:00
net net: dsa: Do not make user port errors fatal 2020-05-20 08:20:03 +02:00
samples vmalloc: fix remap_vmalloc_range() bounds checks 2020-04-29 16:33:14 +02:00
scripts scripts/decodecode: fix trapping instruction formatting 2020-05-14 07:58:29 +02:00
security selinux: properly handle multiple messages in selinux_netlink_send() 2020-05-06 08:15:17 +02:00
sound ALSA: hda: Match both PCI ID and SSID for driver blacklist 2020-05-10 10:31:31 +02:00
tools objtool: Fix stack offset tracking for indirect CFAs 2020-05-14 07:58:29 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm64: Fix 32bit PC wrap-around 2020-05-14 07:58:26 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.41 2020-05-14 07:58:30 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.