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| author | Tejun Heo <tj@kernel.org> | 2017-03-01 21:39:07 +0100 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2017-03-06 21:11:29 +0100 |
| commit | 1d18c2747f937f1b5ec65ce6bf4ccb9ca1aea9e8 (patch) | |
| tree | cee31a8f4ca8c471f296df650c8072e4c96a7855 /kernel/cgroup/pids.c | |
| parent | cgroup: Fix indenting in PID controller documentation (diff) | |
| download | linux-1d18c2747f937f1b5ec65ce6bf4ccb9ca1aea9e8.tar.xz linux-1d18c2747f937f1b5ec65ce6bf4ccb9ca1aea9e8.zip | |
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,
135b8b37bd91 ("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: 135b8b37bd91 ("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>
Diffstat (limited to 'kernel/cgroup/pids.c')
| -rw-r--r-- | kernel/cgroup/pids.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/cgroup/pids.c b/kernel/cgroup/pids.c index e756dae49300..2237201d66d5 100644 --- a/kernel/cgroup/pids.c +++ b/kernel/cgroup/pids.c @@ -229,7 +229,7 @@ static int pids_can_fork(struct task_struct *task) /* Only log the first time events_limit is incremented. */ if (atomic64_inc_return(&pids->events_limit) == 1) { pr_info("cgroup: fork rejected by pids controller in "); - pr_cont_cgroup_path(task_cgroup(current, pids_cgrp_id)); + pr_cont_cgroup_path(css->cgroup); pr_cont("\n"); } cgroup_file_notify(&pids->events_file); |