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

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Message-ID: <CANN689G2Mv+1zr0MgF17uA2GwKaCcEp-ckE=j5YzXHBxjP0tLA@mail.gmail.com>
Date:	Tue, 11 Mar 2014 14:59:47 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	Davidlohr Bueso <davidlohr@...com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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 Tue, Mar 11, 2014 at 1:07 PM, Davidlohr Bueso <davidlohr@...com> wrote:
> On Tue, 2014-03-11 at 15:39 -0400, Sasha Levin wrote:

>> I've ended up deleting the log file by mistake, but this bug does seem to be important
>> so I'd rather not wait before the same issue is triggered again.
>>
>> The call chain is:
>>
>>       mlock (mm/mlock.c:745)
>>               __mm_populate (mm/mlock.c:700)
>>                       __mlock_vma_pages_range (mm/mlock.c:229)
>>                               VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
>
> So __mm_populate() is only called by mlock(2) and this VM_BUG_ON seems
> wrong as we call it without the lock held:

Not related to the bug, but please note that __mm_populate() is public
and has other call sites outside of mlock.c - namely, it is called
during mmap with MAP_POPULATE.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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