mm/oom_kill: wake futex waiters before annihilating victim shared mutex

mm/oom_kill: wake futex waiters before annihilating victim shared mutex

In the case that two or more processes share a futex located within a
shared mmaped region, such as a process that shares a lock between itself
and a number of child processes, we have observed that when a process
holding the lock is oom killed, at least one waiter is never alerted to
this new development and simply continues to wait.

This is visible via pthreads by checking the __owner field of the
pthread_mutex_t structure within a waiting process, perhaps with gdb.

We identify reproduction of this issue by checking a waiting process of a
test program and viewing the contents of the pthread_mutex_t, taking note
of the value in the owner field, and then checking dmesg to see if the
owner has already been killed.

This issue can be tricky to reproduce, but with the modifications of this
small patch, I have found it to be impossible to reproduce.  There may be
additional considerations that I have not taken into account in this patch
and I welcome any comments and criticism.

Link: https://lkml.kernel.org/r/20211208181714.880312-1-jsavitz@redhat.com
Co-developed-by: Nico Pache <npache@redhat.com>
Signed-off-by: Nico Pache <npache@redhat.com>
Signed-off-by: Joel Savitz <jsavitz@redhat.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Darren Hart <dvhart@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andr Almeida <andrealmeid@collabora.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>