linux-kernel - Re: [PATCH v2] issue storage device flush via sync

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Date:	Thu, 26 Mar 2009 23:30:22 -0400
From:	Theodore Tso <tytso@....edu>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] issue storage device flush via sync_blockdev()

On Thu, Mar 26, 2009 at 11:17:44PM -0400, Jeff Garzik wrote:
> Theodore Tso wrote:
>> Jeff,
>>
>> FYI, I tried your patch; it causes the lvm process called out of
>> the initramfs from an Ubuntu 8.10 system to blow up while trying to
>> set up the root filesystem.  The stack trace was:
>>
>> generic_make_request+0x2a3/0x2e6
>> trace_hardirqs_on_caller+0x111/0x135
>> mempool_alloc_slab+0xe/0x10
>> mempool_alloc+0x42/0xe0
>> submit_bio+0xad/0xb5
>> bio_alloc_bioset+0x21/0xfc
>> blkdev_issue_flush+0x7f/0xfc
>> syn_blockdev+0x2a/0x36
>> __blkdev_put_0x44/0x131
>> blkdev_put+0xa/0xc
>> blkdev_close+0x2e/0x32
>> __fput+0xcf/0x15f
>> fput+0x19/0x1b
>> filp_close+0x51/0x5b
>> sys_close+0x73/0xad
>
> hmmm, I wonder if DM/LVM doesn't like blkdev_issue_flush, or it's too  
> early, or what.  I'll toss Ubuntu onto a VM and check it out...

I forgot to mention.  The failure was the EIP was NULL; so it looks
like we called a null function pointer.  The only function pointer
derference I can find is q->make_request_fn() in line 1460 of
blk-core.c, in __generic_make_request.  But that doesn't seem make any
sense....  

Anyway, maybe you can figure out what's going on.  The problem
disappeared as soon as I popped off this patch, though, so it was
pretty clearly the culprit.

					- Ted
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