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Filename Latest commit message Latest commit date
Roman Gushchin 00d484f354 mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm()
We've encountered a rcu stall in get_mem_cgroup_from_mm():

  rcu: INFO: rcu_sched self-detected stall on CPU
  rcu: 33-....: (21000 ticks this GP) idle=6c6/1/0x4000000000000002 softirq=35441/35441 fqs=5017
  (t=21031 jiffies g=324821 q=95837) NMI backtrace for cpu 33
  <...>
  RIP: 0010:get_mem_cgroup_from_mm+0x2f/0x90
  <...>
   __memcg_kmem_charge+0x55/0x140
   __alloc_pages_nodemask+0x267/0x320
   pipe_write+0x1ad/0x400
   new_sync_write+0x127/0x1c0
   __kernel_write+0x4f/0xf0
   dump_emit+0x91/0xc0
   writenote+0xa0/0xc0
   elf_core_dump+0x11af/0x1430
   do_coredump+0xc65/0xee0
   get_signal+0x132/0x7c0
   do_signal+0x36/0x640
   exit_to_usermode_loop+0x61/0xd0
   do_syscall_64+0xd4/0x100
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

The problem is caused by an exiting task which is associated with an
offline memcg.  We're iterating over and over in the do {} while
(!css_tryget_online()) loop, but obviously the memcg won't become online
and the exiting task won't be migrated to a live memcg.

Let's fix it by switching from css_tryget_online() to css_tryget().

As css_tryget_online() cannot guarantee that the memcg won't go offline,
the check is usually useless, except some rare cases when for example it
determines if something should be presented to a user.

A similar problem is described by commit 18fa84a2db ("cgroup: Use
css_tryget() instead of css_tryget_online() in task_get_css()").

Johannes:

: The bug aside, it doesn't matter whether the cgroup is online for the
: callers.  It used to matter when offlining needed to evacuate all charges
: from the memcg, and so needed to prevent new ones from showing up, but we
: don't care now.

Link: http://lkml.kernel.org/r/20191106225131.3543616-1-guro@fb.com
Signed-off-by: Roman Gushchin <guro@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Shakeel Butt <shakeeb@google.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutn <mkoutny@suse.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-11-15 18:34:00 -08:00
arch A fix & simplification for SGI IP27 exception handlers, and a small 2019-11-15 09:10:13 -08:00
block blkcg: make blkcg_print_stat() print stats only for online blkgs 2019-11-06 17:08:38 -07:00
certs
crypto
Documentation Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-11-12 10:53:24 -08:00
drivers Two fixes for the buffered reads and O_DIRECT writes serialization 2019-11-15 10:30:24 -08:00
fs Two fixes for the buffered reads and O_DIRECT writes serialization 2019-11-15 10:30:24 -08:00
include Bugfixes: unwinding of KVM_CREATE_VM failure, 2019-11-12 13:19:15 -08:00
init
ipc
kernel Merge branch 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-11-15 08:44:08 -08:00
lib lib/xz: fix XZ_DYNALLOC to avoid useless memory reallocations 2019-11-15 18:34:00 -08:00
LICENSES
mm mm: memcg: switch to css_tryget() in get_mem_cgroup_from_mm() 2019-11-15 18:34:00 -08:00
net vsock/virtio: fix sock refcnt holding during the shutdown 2019-11-08 12:17:50 -08:00
samples samples/bpf: fix build by setting HAVE_ATTR_TEST to zero 2019-10-31 21:39:15 +01:00
scripts arm64 fix for -rc8 / final 2019-11-15 09:14:23 -08:00
security efi/efi_test: Lock down /dev/efi_test and require CAP_SYS_ADMIN 2019-10-31 09:40:21 +01:00
sound ALSA: usb-audio: Fix incorrect size check for processing/extension units 2019-11-14 18:01:22 +01:00
tools selftests: kvm: fix build with glibc >= 2.30 2019-11-13 15:48:00 +01:00
usr
virt KVM: Add a comment describing the /dev/kvm no_compat handling 2019-11-15 10:14:04 +01:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS A fix & simplification for SGI IP27 exception handlers, and a small 2019-11-15 09:10:13 -08:00
Makefile kbuild: tell sparse about the $ARCH 2019-11-15 00:13:23 +09:00
README

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

There are several guides for kernel developers and users. These guides can
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In order to build the documentation, use ``make htmldocs`` or
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    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.