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Johannes Weiner cd324edce5 mm: memcontrol: handle div0 crash race condition in memory.low 
Tejun reports seeing rare div0 crashes in memory.low stress testing:

  RIP: 0010:mem_cgroup_calculate_protection+0xed/0x150
  Code: 0f 46 d1 4c 39 d8 72 57 f6 05 16 d6 42 01 40 74 1f 4c 39 d8 76 1a 4c 39 d1 76 15 4c 29 d1 4c 29 d8 4d 29 d9 31 d2 48 0f af c1 <49> f7 f1 49 01 c2 4c 89 96 38 01 00 00 5d c3 48 0f af c7 31 d2 49
  RSP: 0018:ffffa14e01d6fcd0 EFLAGS: 00010246
  RAX: 000000000243e384 RBX: 0000000000000000 RCX: 0000000000008f4b
  RDX: 0000000000000000 RSI: ffff8b89bee84000 RDI: 0000000000000000
  RBP: ffffa14e01d6fcd0 R08: ffff8b89ca7d40f8 R09: 0000000000000000
  R10: 0000000000000000 R11: 00000000006422f7 R12: 0000000000000000
  R13: ffff8b89d9617000 R14: ffff8b89bee84000 R15: ffffa14e01d6fdb8
  FS:  0000000000000000(0000) GS:ffff8b8a1f1c0000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f93b1fc175b CR3: 000000016100a000 CR4: 0000000000340ea0
  Call Trace:
    shrink_node+0x1e5/0x6c0
    balance_pgdat+0x32d/0x5f0
    kswapd+0x1d7/0x3d0
    kthread+0x11c/0x160
    ret_from_fork+0x1f/0x30

This happens when parent_usage == siblings_protected.

We check that usage is bigger than protected, which should imply
parent_usage being bigger than siblings_protected.  However, we don't
read (or even update) these values atomically, and they can be out of
sync as the memory state changes under us.  A bit of fluctuation around
the target protection isn't a big deal, but we need to handle the div0
case.

Check the parent state explicitly to make sure we have a reasonable
positive value for the divisor.

Link: http://lkml.kernel.org/r/20200615140658.601684-1-hannes@cmpxchg.org
Fixes: 8a931f8013 ("mm: memcontrol: recursive memory.low protection")
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Tejun Heo <tj@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Chris Down <chris@chrisdown.name>
Cc: Roman Gushchin <guro@fb.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-26 00:27:37 -07:00
arch openrisc: fix boot oops when DEBUG_VM is enabled 2020-06-26 00:27:36 -07:00
block block-5.8-2020-06-19 2020-06-19 13:11:26 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: drbg - always try to free Jitter RNG instance 2020-06-15 17:38:54 +10:00
Documentation spi: Fixes for v5.8 2020-06-22 09:49:59 -07:00
drivers media: omap3isp: remove cacheflush.h 2020-06-26 00:27:37 -07:00
fs ocfs2: fix value of OCFS2_INVALID_SLOT 2020-06-26 00:27:37 -07:00
include make asm-generic/cacheflush.h more standalone 2020-06-26 00:27:37 -07:00
init Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel kexec: do not verify the signature without the lockdown or mandatory signature 2020-06-26 00:27:36 -07:00
lib lib: fix test_hmm.c reference after free 2020-06-26 00:27:37 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm: memcontrol: handle div0 crash race condition in memory.low 2020-06-26 00:27:37 -07:00
net An important follow-up for replica reads support that went into -rc1 2020-06-19 12:25:04 -07:00
samples Kbuild fixes for v5.8 2020-06-21 12:44:52 -07:00
scripts Kbuild fixes for v5.8 2020-06-21 12:44:52 -07:00
security selinux/stable-5.8 PR 20200621 2020-06-21 15:41:24 -07:00
sound sound fixes for 5.8-rc3 2020-06-25 09:15:24 -07:00
tools virtio: fixes, tests 2020-06-24 14:26:28 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt MIPS: 2020-06-12 11:05:52 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: generate vmlinux.symvers and reuse it for the second modpost 2020-06-06 23:38:12 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2020-06-20 19:18:27 -07:00
Makefile Linux 5.8-rc2 2020-06-21 15:45:29 -07:00
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.