Re: crash during oom reaper

[Michal Hocko]

On Sun 18-12-16 22:47:07, Tetsuo Handa wrote:
> On 2016/12/16 22:14, Michal Hocko wrote:
[...]
> > I would have to rememeber all the details. This is mostly off-topic for
> > this particular thread so I think it would be better if you could send a
> > full patch separatelly and we can discuss it there?
> > 
> 
> zap_page_range() calls mmu_notifier_invalidate_range_start().
> mmu_notifier_invalidate_range_start() calls __mmu_notifier_invalidate_range_start().
> __mmu_notifier_invalidate_range_start() calls srcu_read_lock()/srcu_read_unlock().
> This means that zap_page_range() might sleep.
> 
> I don't know what individual notifier will do, but for example
> 
>   static const struct mmu_notifier_ops i915_gem_userptr_notifier = {
>           .invalidate_range_start = i915_gem_userptr_mn_invalidate_range_start,
>   };
> 
> i915_gem_userptr_mn_invalidate_range_start() calls flush_workqueue()
> which means that we can OOM livelock if work item involves memory allocation.
> Some of other notifiers call mutex_lock()/mutex_unlock().
> 
> Even if none of currently in-tree notifier users are blocked on memory
> allocation, I think it is not guaranteed that future changes/users won't be
> blocked on memory allocation.

Kirill has sent this as a separate patchset [1]. Could you follow up on
that there please?

http://lkml.kernel.org/r/20161216141556.75130-4-kirill.shutemov@xxxxxxxxxxxxxxx

-- 
Michal Hocko
SUSE Labs