linux-kernel - Re: [4.1-rc7] btrfs related VM_BUG

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Message-ID: <20150630192844.GA2569@codemonkey.org.uk>
Date:	Tue, 30 Jun 2015 15:28:44 -0400
From:	Dave Jones <davej@...emonkey.org.uk>
To:	Josef Bacik <jbacik@...com>
Cc:	Chris Mason <clm@...com>, dsterba@...e.cz,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [4.1-rc7] btrfs related VM_BUG_ON in filemap.c

On Tue, Jun 30, 2015 at 03:23:00PM -0400, Josef Bacik wrote:
 > On 06/30/2015 03:20 PM, Dave Jones wrote:
 > > On Wed, Jun 17, 2015 at 09:35:41AM -0400, Dave Jones wrote:
 > >
 > >   > page:ffffea00027cc640 count:4 mapcount:0 mapping:ffff8800af11d8a0 index:0x0
 > >   > flags: 0x4000000000000846(error|referenced|active|private)
 > >   > page dumped because: VM_BUG_ON_PAGE(!PageLocked(page))
 > >   > ------------[ cut here ]------------
 > >   > kernel BUG at mm/filemap.c:745!
 > > 
 > > Still occasionally bumping into this.
 > > The 'count:4 mapcount:0' is constant in every instance I've seen
 > > so far. Could that be a clue ?
 > >
 > > I've seen various page flags, but it's always !locked
 > >
 > > Ideas on additional debugging I could add ?
 > 
 > Huh I just noticed that PG_Error seems to be set, is that the same for 
 > every time?  I wonder where that's getting set and why.  I'll dig into 
 > the areas we set that and see if I can spot anything.  Thanks,

Seems to be set every time yeah.
I can try annotating those places that set it to see which one is triggering
when I get home.

	Dave

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