Re: [PATCH] oom: Make coredump interruptible

[Oleg Nesterov <oleg@redhat.com>]

On 06/02, Roland McGrath wrote:
>
> > when select_bad_process() finds the task P to kill it can participate
> > in the core dump (sleep in exit_mm), but we should somehow inform the
> > thread which actually dumps the core: P->mm->core_state->dumper.
>
> Perhaps it should simply do that: if you would choose P to oom-kill, and
> P->mm->core_state!=NULL, then choose P->mm->core_state->dumper instead.

... to set TIF_MEMDIE which should be checked in elf_core_dump().

Probably yes.

> > Well, we can use TIF_MEMDIE if we chose the right thread, I think.
> > But perhaps mm->flags |= MMF_OOM is better, it can have other user.
> > I dunno.
>
> This is all the quick hack before get around to just making core dumping
> fully-interruptible, no?  So we should go with whatever is the simplest
> change now.

Yes.

> Perhaps this belongs in another thread as you suggested.  But I wonder what
> we might get just from s/TASK_UNINTERRUPTIBLE/TASK_KILLABLE/ in exit_mm.

Oh. This needs more thinking. Definitely the task sleeping in exit_mm()
must not exit until core_state->dumper->thread returns from do_coredump().
If nothing else, the dumper can use its task_struct and it relies on
the stable core_thread->next list. And right now TASK_KILLABLE can't
work anyway, it is possible that fatal_signal_pending() is true.

But perhaps we can do something later. Assuming that do_coredump() is
interruptible, TASK_KILLABLE can make the difference only if the dumper
belongs to another thread-group.

Oleg.