Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write_failed lockup

[Sergey Senozhatsky]

Hello,

On (06/03/16 15:49), Michal Hocko wrote:
> __khugepaged_exit is called during the final __mmput and it employs a
> complex synchronization dances to make sure it doesn't race with the
> khugepaged which might be scanning this mm at the same time. This is
> all caused by the fact that khugepaged doesn't pin mm_users. Things
> would simplify considerably if we simply check the mm at
> khugepaged_scan_mm_slot and if mm_users was already 0 then we know it
> is dead and we can unhash the mm_slot and move on to another one. This
> will also guarantee that __khugepaged_exit cannot race with khugepaged
> and so we can free up the slot if it is still hashed.
> 
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

with this patch and
http://ozlabs.org/~akpm/mmotm/broken-out/mm-thp-make-swapin-readahead-under-down_read-of-mmap_sem-fix-2.patch

I saw no problems during my tests (well, may be didn't test hard
enough).

	-ss