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

On Sat 04-06-16 16:51:14, Sergey Senozhatsky wrote:

Hello,

On (06/03/16 15:49), Michal Hocko wrote:

quoted

__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@suse.com>

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).

Thanks for the testing!
-- 
Michal Hocko
SUSE Labs

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