mm: memcontrol: fix potential oom_lock recursion deadlock

syzbot is reporting GFP_KERNEL allocation with oom_lock held when
reporting memcg OOM [1].  If this allocation triggers the global OOM
situation then the system can livelock because the GFP_KERNEL
allocation with oom_lock held cannot trigger the global OOM killer
because __alloc_pages_may_oom() fails to hold oom_lock.

Fix this problem by removing the allocation from memory_stat_format()
completely, and pass static buffer when calling from memcg OOM path.

Note that the caller holding filesystem lock was the trigger for syzbot
to report this locking dependency.  Doing GFP_KERNEL allocation with
filesystem lock held can deadlock the system even without involving OOM
situation.

Link: https://syzkaller.appspot.com/bug?extid=2d2aeadc6ce1e1f11d45 [1]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: c8713d0b23123759 ("mm: memcontrol: dump memory.stat during cgroup OOM")
Signed-off-by: Tetsuo Handa <[email protected]>
Reported-by: syzbot <[email protected]>
Suggested-by: Michal Hocko <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions