Re: !PageLocked BUG_ON hit in clear_page_dirty_for_io

From: Chris Mason <clm@fb.com>
To: Dave Jones <davej@codemonkey.org.uk>
Cc: <jbacik@fb.com>, <dsterba@suse.com>, <linux-btrfs@vger.kernel.org>
Subject: Re: !PageLocked BUG_ON hit in clear_page_dirty_for_io
Date: Thu, 10 Dec 2015 16:30:24 -0500	[thread overview]
Message-ID: <20151210213024.GC11257@ret.masoncoding.com> (raw)
In-Reply-To: <20151210193555.GA23535@codemonkey.org.uk>

On Thu, Dec 10, 2015 at 02:35:55PM -0500, Dave Jones wrote:
> On Thu, Dec 10, 2015 at 02:02:20PM -0500, Chris Mason wrote:
>  > On Tue, Dec 08, 2015 at 11:25:28PM -0500, Dave Jones wrote:
>  > > Not sure if I've already reported this one, but I've been seeing this
>  > > a lot this last couple days.
>  > > 
>  > > kernel BUG at mm/page-writeback.c:2654!
>  > > invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC KASAN
>  > > CPU: 1 PID: 2566 Comm: trinity-c1 Tainted: G        W       4.4.0-rc4-think+ #14
>  > > task: ffff880462811b80 ti: ffff8800cd808000 task.ti: ffff8800cd808000
>  > > RIP: 0010:[<ffffffff8826ff40>]  [<ffffffff8826ff40>] clear_page_dirty_for_io+0x180/0x1d0
>  > 
>  > Huh, are you able to reproduce at will?  From this code path it should
>  > mean somebody else is unlocking a page they don't own.
> 
> pretty easily yeah. I hit it maybe a couple dozen times yesterday.
> So if you've got some idea of printk's to spray anywhere I can give
> that a shot.

I'd rather try to trigger it here.  Going to have to add some way to
record which stack trace last unlocked and/or freed the page.

-chris