linux-kernel - Re: mm: mmap_sem lock assertion failure in __mlock_vma_pages

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Message-ID: <531F73AB.5060402@oracle.com>
Date:	Tue, 11 Mar 2014 16:35:55 -0400
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Davidlohr Bueso <davidlohr@...com>
CC:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: mm: mmap_sem lock assertion failure in __mlock_vma_pages_range

On 03/11/2014 04:30 PM, Andrew Morton wrote:
> I worry about what happens if __get_user_pages decides to do
>
> 				if (ret & VM_FAULT_RETRY) {
> 					if (nonblocking)
> 						*nonblocking = 0;
> 					return i;
> 				}
>
> uh-oh, that just cleared __mm_populate()'s `locked' variable and we'll
> forget to undo mmap_sem.  That won't explain this result, but it's a
> potential problem.

That's actually seems right because if 'ret & VM_FAULT_RETRY' is true it means that
lock_page_or_retry() was supposed to release mmap_sem for us.


Thanks,
Sasha
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