linux-kernel - Re: 32-bit bio regression with 4.3 [was: Re: cgroup/loop Bad page state oops in Linux v4.2-rc3-136-g45b4b782e848]

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Date:	Sat, 12 Sep 2015 00:34:19 -0700
From:	Ming Lin <mlin@...nel.org>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	Joe Thornber <ejt@...hat.com>,
	Ming Lei <ming.lei@...onical.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...com>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	awilliam@...hat.com
Subject: Re: 32-bit bio regression with 4.3 [was: Re: cgroup/loop Bad page
 state oops in Linux v4.2-rc3-136-g45b4b782e848]

On Fri, 2015-09-11 at 21:43 -0700, Ming Lin wrote:
> On Fri, Sep 11, 2015 at 2:43 PM, Mike Snitzer <snitzer@...hat.com> wrote:
> > Ming, Jens, others:
> >
> > Please see this BZ comment that speaks to a 4.3 regression due to the
> > late bio splitting changes:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1247382#c41
> >
> > But inlined here so we can continue on list:
> > (In reply to Josh Boyer from comment #40)
> >> The function that was fixed in 4.2 doesn't exist any longer in
> >> 4.3.0-0.rc0.git6.1.fc24.  That kernel corresponds to Linux
> >> v4.2-6105-gdd5cdb48edfd which contains commit
> >> 8ae126660fddbeebb9251a174e6fa45b6ad8f932, which removed it completely.  So
> >> whatever fix was made in dm_merge_bvec doesn't seem to have made it to
> >> whatever replaced it.
> >
> > The dm core fix to dm_merge_bvec was commit bd4aaf8f9b ("dm: fix
> > dm_merge_bvec regression on 32 bit systems").  But I'm not sure there is
> > a clear equivalent in the late bio splitting code that replaced block
> > core's merge_bvec logic.
> >
> > merge_bvec was all about limiting bios (by asking "can/should this page
> > be added to this bio?") whereas the late bio splitting is more "build
> > the bios as large as possible and worry about splitting later".
> >
> > Regardless, this regression needs to be reported to Ming Lin
> > <ming.l@....samsung.com>, Jens Axboe and the others involved in
> > maintaining the late bio splitting changes in block core.
> 
> I'm looking at it now.

I tried rawhide-20150903 boot.iso and rawhide-20150904 boot.iso.
0903 boot.iso is OK, but 0904 boot.iso just stuck at "Reached target
Basic System". So I can't see the panic.
http://www.minggr.net/pub/20150912/rawhide-20150904-boot.iso.png

I'll run test on 32bit VM, see if I can reproduce the bug.

Adam,

Could you also help to confirm that commit 7140aaf is OK and commit
8ae1266 is bad?

Thanks,
Ming


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