linux-kernel - Re: Strange block/scsi/workqueue issue

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Date:	Tue, 12 Apr 2011 14:56:56 -0500
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Steven Whitehouse <swhiteho@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Jens Axboe <jaxboe@...ionio.com>
Subject: Re: Strange block/scsi/workqueue issue

On Tue, 2011-04-12 at 19:33 +0100, Steven Whitehouse wrote:
> Hi,
> 
> On Tue, 2011-04-12 at 12:41 -0500, James Bottomley wrote:
> > On Tue, 2011-04-12 at 17:51 +0100, Steven Whitehouse wrote:
> > > Still not quite there, but looking more hopeful now,
> > 
> > Not sure I share your optimism; but this one
> > 
> Neither do I any more :-) Looks like we are back in blk_peek_request()
> again. 
[...]
>                 if (!q->elevator->ops || !q->elevator->ops->elevator_dispatch_fn
> (q, 0))
>     6d62:       49 8b 44 24 18          mov    0x18(%r12),%rax
>     6d67:       48 8b 00                mov    (%rax),%rax
>     6d6a:       48 85 c0                test   %rax,%rax
>     6d6d:       74 0c                   je     6d7b <blk_peek_request+0x11b>
>     6d6f:       31 f6                   xor    %esi,%esi
>     6d71:       4c 89 e7                mov    %r12,%rdi                                <----- here
>     6d74:       ff 50 28                callq  *0x28(%rax)
>     6d77:       85 c0                   test   %eax,%eax
>     6d79:       75 da                   jne    6d55 <blk_peek_request+0xf5>
>     6d7b:       45 31 ed                xor    %r13d,%r13d

Hmm, wrong signal for no elevator then.  How about this?

James

---

Index: BUILD-2.6/block/blk.h
===================================================================
--- BUILD-2.6.orig/block/blk.h	2011-04-12 14:51:35.000000000 -0500
+++ BUILD-2.6/block/blk.h	2011-04-12 14:51:53.000000000 -0500
@@ -62,7 +62,8 @@ static inline struct request *__elv_next
 			return rq;
 		}
 
-		if (!q->elevator->ops || !q->elevator->ops->elevator_dispatch_fn(q, 0))
+		if (test_bit(QUEUE_FLAG_DEAD, &q->queue_flags) ||
+		    !q->elevator->ops->elevator_dispatch_fn(q, 0))
 			return NULL;
 	}
 }


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