cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should be atomic flags
authorZefan Li <lizefan@huawei.com>
Thu, 25 Sep 2014 01:41:02 +0000 (09:41 +0800)
committerTejun Heo <tj@kernel.org>
Thu, 25 Sep 2014 02:16:06 +0000 (22:16 -0400)
commit2ad654bc5e2b211e92f66da1d819e47d79a866f0
treec638346ac104f054fc61649a8739b004d06aff59
parente0e5070b20e01f0321f97db4e4e174f3f6b49e50
cpuset: PF_SPREAD_PAGE and PF_SPREAD_SLAB should be atomic flags

When we change cpuset.memory_spread_{page,slab}, cpuset will flip
PF_SPREAD_{PAGE,SLAB} bit of tsk->flags for each task in that cpuset.
This should be done using atomic bitops, but currently we don't,
which is broken.

Tetsuo reported a hard-to-reproduce kernel crash on RHEL6, which happened
when one thread tried to clear PF_USED_MATH while at the same time another
thread tried to flip PF_SPREAD_PAGE/PF_SPREAD_SLAB. They both operate on
the same task.

Here's the full report:
https://lkml.org/lkml/2014/9/19/230

To fix this, we make PF_SPREAD_PAGE and PF_SPREAD_SLAB atomic flags.

v4:
- updated mm/slab.c. (Fengguang Wu)
- updated Documentation.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: Kees Cook <keescook@chromium.org>
Fixes: 950592f7b991 ("cpusets: update tasks' page/slab spread flags in time")
Cc: <stable@vger.kernel.org> # 2.6.31+
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Zefan Li <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Documentation/cgroups/cpusets.txt
include/linux/cpuset.h
include/linux/sched.h
kernel/cpuset.c
mm/slab.c