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Date: Mon, 9 Jun 2008 11:34:46 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Vegard Nossum <vegard.nossum@gmail.com>,
       Kay Sievers <kay.sievers@vrfy.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
       Jens Axboe <jens.axboe@oracle.com>, Greg Kroah-Hartman <gregkh@suse.de>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       "Rafael J. Wysocki" <rjw@sisk.pl>
Subject: Re: [bug, 2.6.26-rc4/rc5] sporadic bootup crashes in
	blk_lookup_devt()/prepare_namespace()
Message-ID: <20080609093446.GA31803@elte.hu>
References: <20080609080312.GA32458@elte.hu> <20080609020623.b6727f2b.akpm@linux-foundation.org> <19f34abd0806090209l541d93c6jaba2704314b34418@mail.gmail.com>
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* Vegard Nossum <vegard.nossum@gmail.com> wrote:

> On Mon, Jun 9, 2008 at 11:06 AM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Mon, 9 Jun 2008 10:03:12 +0200 Ingo Molnar <mingo@elte.hu> wrote:
> >
> >> -tip testing has started triggering a new type of sporadic bootup crash
> >> a few days ago. Find below a collection of 14 crashes i've managed to
> >> capture so far, which are all similar to this crash pattern:
> >>
> >>  BUG: unable to handle kernel paging request at ffff81003b984fb8
> >>  IP: [<ffffffff803fafd4>] blk_lookup_devt+0x42/0xa0
> >>  PGD 8063 PUD 9063 PMD 3be2d163 PTE 800000003b984160
> >>  Oops: 0000 [1] SMP DEBUG_PAGEALLOC
> >>
> >>  Call Trace:
> >>   [<ffffffff80bac17b>] ? ip_auto_config+0x0/0xd94
> >>   [<ffffffff80209259>] name_to_dev_t+0x145/0xeec
> >>   [<ffffffff803ff2be>] ? __next_cpu_nr+0x22/0x2b
> >>   [<ffffffff80b7f372>] prepare_namespace+0x91/0x14c
> >>   [<ffffffff80b7eb70>] kernel_init+0x2fe/0x314
> >>   [<ffffffff80251f3d>] ? trace_hardirqs_on_caller+0xca/0xee
> >>   [<ffffffff80741bbb>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> >>   [<ffffffff80251f3d>] ? trace_hardirqs_on_caller+0xca/0xee
> >>   [<ffffffff8020d3f8>] child_rip+0xa/0x12
> >>   [<ffffffff8020c90c>] ? restore_args+0x0/0x30
> >>   [<ffffffff8025068d>] ? trace_hardirqs_off+0xd/0xf
> >>   [<ffffffff80b7e872>] ? kernel_init+0x0/0x314
> >>   [<ffffffff8020d3ee>] ? child_rip+0x0/0x12
> >
> > Did you work out where it's dying?  Deref of `dev' I assume?
> 
>                         struct gendisk *disk = dev_to_disk(dev);

wild shot in the dark: if i were to finger a random commit in this 
general code area where it crashed it would be:

| commit 30f2f0eb4bd2c43d10a8b0d872c6e5ad8f31c9a0
| Author: Kay Sievers <kay.sievers@vrfy.org>
| Date:   Tue May 6 22:31:33 2008 +0200
|
|     block: do_mounts - accept root=<non-existant partition>

i could try a revert of this commit although given the extremely 
sporadic nature of this bug i doubt i could do any conclusive testing.

	Ingo
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