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Date: Mon, 6 Jun 2016 10:39:46 +0200
From: Michal Hocko <mhocko@...nel.org>
To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Stephen Rothwell <sfr@...b.auug.org.au>, linux-mm@...ck.org,
linux-next@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: 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:
> > __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@...e.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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