linux-kernel - Re: [linux-next: Tree for Jun 1] __khugepaged_exit rwsem_down_write

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Date:	Fri, 3 Jun 2016 16:15:51 +0900
From:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.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,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [linux-next: Tree for Jun 1] __khugepaged_exit
 rwsem_down_write_failed lockup

Hello,

On (06/02/16 11:21), Michal Hocko wrote:
[..]
> @@ -2863,6 +2854,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
>  
>  		collect_mm_slot(mm_slot);
>  	}
> +	mmput(mm);
>  
>  	return progress;
>  }

this possibly sleeping mmput() is called from
under the spin_lock(&khugepaged_mm_lock).

there is also a trivial build fixup needed
(move collect_mm_slot() before __khugepaged_exit()).


it's quite hard to trigger the bug (somehow), so I can't
follow up with more information as of now.

	-ss