linux-kernel - Re: 3.15rc2 hanging processes on exit.

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Date:	Wed, 23 Apr 2014 08:07:16 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>, Hugh Dickins <hughd@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: 3.15rc2 hanging processes on exit.

On Wed, Apr 23, 2014 at 7:49 AM, Dave Jones <davej@...hat.com> wrote:
>
> So for reasons I can't figure out, I've not been able to hit it on 3.14
> The only 'interesting' thing I've hit in overnight testing is this, which
> I'm not sure if I've also seen in my .15rc testing, but it doesn't look
> familiar to me.  (Though the vm oopses I've seen the last few months
> are starting to all blur together in my memory)
>
>
> kernel BUG at mm/mlock.c:82!

That's

  mlock_vma_page:
    BUG_ON(!PageLocked(page));

which is odd, because:

> Call Trace:
>  [<ffffffffbe196612>] try_to_unmap_nonlinear+0x2a2/0x530
>  [<ffffffffbe1972a7>] rmap_walk+0x157/0x320
>  [<ffffffffbe1976e3>] try_to_unmap+0x93/0xf0
>  [<ffffffffbe1bb8f6>] migrate_pages+0x3b6/0x7b0

All the calls to "try_to_unmap()" in mm/migrate.c are preceded by the pattern

        if (!trylock_page(page)) {
                 ....
                lock_page(page);
        }

where there are just a few "goto out" style cases for the "ok, we're
not going to wait for this page lock" in there.

Very odd.  Does anybody see anything I missed?

              Linus
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