oom_kill.c: futex: delay the OOM reaper to allow time for proper futex cleanup
The pthread struct is allocated on PRIVATE|ANONYMOUS memory [1] which
can be targeted by the oom reaper. This mapping is used to store the
futex robust list head; the kernel does not keep a copy of the robust
list and instead references a userspace address to maintain the
robustness during a process death.
A race can occur between exit_mm and the oom reaper that allows the oom
reaper to free the memory of the futex robust list before the exit path
has handled the futex death:
CPU1 CPU2
--------------------------------------------------------------------
page_fault
do_exit "signal"
wake_oom_reaper
oom_reaper
oom_reap_task_mm (invalidates mm)
exit_mm
exit_mm_release
futex_exit_release
futex_cleanup
exit_robust_list
get_user (EFAULT- can't access memory)
If the get_user EFAULT's, the kernel will be unable to recover the
waiters on the robust_list, leaving userspace mutexes hung indefinitely.
Delay the OOM reaper, allowing more time for the exit path to perform
the futex cleanup.
Reproducer: https://gitlab.com/jsavitz/oom_futex_reproducer
Based on a patch by Michal Hocko.
Link: https://elixir.bootlin.com/glibc/glibc-2.35/source/nptl/allocatestack.c#L370 [1]
Link: https://lkml.kernel.org/r/20220414144042.677008-1-npache@redhat.com
Fixes: 212925802454 ("mm: oom: let oom_reap_task and exit_mmap run concurrently")
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Signed-off-by: Nico Pache <npache@redhat.com>
Co-developed-by: Joel Savitz <jsavitz@redhat.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Herton R. Krzesinski <herton@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joel Savitz <jsavitz@redhat.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2 files changed
