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Tejun Heo 1d18c2747f cgroup/pids: remove spurious suspicious RCU usage warning
pids_can_fork() is special in that the css association is guaranteed
to be stable throughout the function and thus doesn't need RCU
protection around task_css access.  When determining the css to charge
the pid, task_css_check() is used to override the RCU sanity check.

While adding a warning message on fork rejection from pids limit,
135b8b37bd ("cgroup: Add pids controller event when fork fails
because of pid limit") incorrectly added a task_css access which is
neither RCU protected or explicitly annotated.  This triggers the
following suspicious RCU usage warning when RCU debugging is enabled.

  cgroup: fork rejected by pids controller in

  ===============================
  [ ERR: suspicious RCU usage.  ]
  4.10.0-work+ #1 Not tainted
  -------------------------------
  ./include/linux/cgroup.h:435 suspicious rcu_dereference_check() usage!

  other info that might help us debug this:

  rcu_scheduler_active = 2, debug_locks = 0
  1 lock held by bash/1748:
   #0:  (&cgroup_threadgroup_rwsem){+++++.}, at: [<ffffffff81052c96>] _do_fork+0xe6/0x6e0

  stack backtrace:
  CPU: 3 PID: 1748 Comm: bash Not tainted 4.10.0-work+ #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc25 04/01/2014
  Call Trace:
   dump_stack+0x68/0x93
   lockdep_rcu_suspicious+0xd7/0x110
   pids_can_fork+0x1c7/0x1d0
   cgroup_can_fork+0x67/0xc0
   copy_process.part.58+0x1709/0x1e90
   _do_fork+0xe6/0x6e0
   SyS_clone+0x19/0x20
   do_syscall_64+0x5c/0x140
   entry_SYSCALL64_slow_path+0x25/0x25
  RIP: 0033:0x7f7853fab93a
  RSP: 002b:00007ffc12d05c90 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f7853fab93a
  RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
  RBP: 00007ffc12d05cc0 R08: 0000000000000000 R09: 00007f78548db700
  R10: 00007f78548db9d0 R11: 0000000000000246 R12: 00000000000006d4
  R13: 0000000000000001 R14: 0000000000000000 R15: 000055e3ebe2c04d
  /asdf

There's no reason to dereference task_css again here when the
associated css is already available.  Fix it by replacing the
task_cgroup() call with css->cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Mike Galbraith <efault@gmx.de>
Fixes: 135b8b37bd ("cgroup: Add pids controller event when fork fails because of pid limit")
Cc: Kenny Yu <kennyyu@fb.com>
Cc: stable@vger.kernel.org # v4.8+
Signed-off-by: Tejun Heo <tj@kernel.org>
2017-03-06 15:11:29 -05:00
Documentation cgroup: Fix indenting in PID controller documentation 2017-03-06 14:46:27 -05:00
arch Second batch of KVM changes for 4.11 merge window 2017-03-04 11:36:19 -08:00
block Merge branch 'for-linus' of git://git.kernel.dk/linux-block 2017-03-03 10:53:35 -08:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2017-03-04 10:42:53 -08:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-04 17:31:39 -08:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-03-03 21:44:35 -08:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-04 17:31:39 -08:00
init sched/headers: Prepare to move _init() prototypes from <linux/sched.h> to <linux/sched/init.h> 2017-03-02 08:42:40 +01:00
ipc Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
kernel cgroup/pids: remove spurious suspicious RCU usage warning 2017-03-06 15:11:29 -05:00
lib Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
mm Merge branch 'rebased-statx' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-03-03 11:38:56 -08:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-04 17:31:39 -08:00
samples Merge branch 'rebased-statx' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2017-03-03 11:38:56 -08:00
scripts objtool, modules: Discard objtool annotation sections for modules 2017-03-01 20:32:25 +01:00
security Merge branch 'WIP.sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-03 10:16:38 -08:00
sound sched/headers: Prepare to move signal wakeup & sigpending methods from <linux/sched.h> into <linux/sched/signal.h> 2017-03-02 08:42:32 +01:00
tools Second batch of KVM changes for 4.11 merge window 2017-03-04 11:36:19 -08:00
usr kbuild: initramfs cleanup, set target from Kconfig 2017-01-05 09:40:16 -08:00
virt Second batch of KVM changes for 4.11 merge window 2017-03-04 11:36:19 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap mailmap: add codeaurora.org names for nameless email commits 2017-01-10 18:31:55 -08:00
COPYING
CREDITS MAINTAINERS: Remove old e-mail address 2017-02-13 12:24:56 -05:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2017-03-04 17:31:39 -08:00
Makefile Linux 4.11-rc1 2017-03-05 12:59:56 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README

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

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

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.