Re: [PATCH] mm/oom_kill: fix hung tasks queued on mmap_lock behind a long reap

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 14 Sep 2026 20:36:16 +0200 Michal Hocko <mhocko@suse.com> wrote:

> > Call Trace:
> >  <TASK>
> >  __schedule+0x487/0x1870
> >  schedule+0x28/0xb0
> >  schedule_preempt_disabled+0x16/0x30
> >  rwsem_down_write_slowpath+0x1d4/0x750
> >  down_write+0x60/0x70
> >  __ksm_exit+0xb4/0x230
> >  __mmput+0x12c/0x150
> >  mmput+0x1e/0x30
> >  do_exit+0x283/0xa30
> >  do_group_exit+0x34/0x90
> >  get_signal+0x952/0x960
> >  arch_do_signal_or_restart+0x41/0x250
> >  exit_to_user_mode_loop+0xd3/0x560
> >  do_syscall_64+0x385/0x470
> >  </TASK>
> > 
> > KSM is just the one LTP happened to hit: __khugepaged_exit() has the
> > same write lock cycle ahead of exit_mmap().
> 
> Why is this a practical problem we need to care about? It is kind of
> natural that the oom victim exit path might race with the oom reaper. They
> share the same lock that is mutualy exclusive. The whole point of the
> reaper is to ensure there is a forward progress achieved. So before we
> start modifying this let's talk about any practical/real life problems.

If this situation is expected, unavoidable etc then perhaps the best
change is to periodically poke the hung-task detector?