linux-kernel - Re: [PATCH 1/1] driver/md/block: Alloc space for member flush

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Date:	Wed, 28 May 2014 11:03:14 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	"Li, Zhen-Hua" <zhen-hual@...com>
Cc:	linux-kernel@...r.kernel.org, Alasdair Kergon <agk@...hat.com>,
	dm-devel@...hat.com, Neil Brown <neilb@...e.de>,
	linux-raid@...r.kernel.org
Subject: Re: [PATCH 1/1] driver/md/block: Alloc space for member flush_rq

On Wed, May 28 2014 at  2:22am -0400,
Li, Zhen-Hua <zhen-hual@...com> wrote:

> This patch is trying to fix a kernel crash bug.
> 
> When kernel boots on a HP large system, it crashes.
> The reason is when blk_rq_init is called, the second parameter rq , which
> is a member as q->flush_rq, is NULL. Kernel does not allocate space for it.
> 
> This fix adds an alloc for flush_rq member when request_queue is created in
> struct mapped_device *alloc_dev(int minor);
> 
> Bug Details:
> Error message:
> 
> [   62.931942] BUG: unable to handle kernel NULL pointer dereference at (null)
> [   62.931949] IP: [<ffffffff812b3f30>] blk_rq_init+0x40/0x160^M
> [   62.931949] PGD 0 ^M
> [   62.931951] Oops: 0002 [#1] SMP

You didn't specify which kernel you're running.  But this was fixed for
v3.15-rc6 via linux.git commit 7982e90c3a5 ("block: fix q->flush_rq NULL
pointer crash on dm-mpath flush").  And then there was the follow-on fix
from linux.git commit 708f04d2ab ("block: free q->flush_rq in
blk_init_allocated_queue error paths")

So all this is to say: Nack to your patch, we've already fixed the issue
differently.
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