linux-kernel - Re: cache flush timeouts by blk_queue

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Date:	Mon, 26 Jan 2009 11:55:40 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Bernd Schubert <bs@...eap.de>
Cc:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: cache flush timeouts by blk_queue_ordered()

On Thu, 20 Nov 2008 19:19:19 +0100
Bernd Schubert <bs@...eap.de> wrote:

> Hello,
> 
> with some FC hardware-raid units we have the problem that the 
> SYNCHRONIZE_CACHE command reproducibly fails. 
> 
> [658715.827428] sd 6:0:2:2: last recovery: 4311805647, now: 4459793681
> [658715.833980] sd 6:0:2:2: [sdk] Result: hostbyte=DID_OK driverbyte=DRIVER_OK,SUGGEST_OK
> [658715.842288] sd 6:0:2:2: [sdk] CDB: Synchronize Cache(10): 35 00 00 00 00 00 00 00 00 00
> [658715.850954] sd 6:0:2:2: Activating scsi error recovery (1)
> [658715.856793] sd 6:0:2:2: trying to abort command
> [658715.861820] qla2xxx 0000:07:02.0: scsi(6:2:2): Abort command issued -- 1 36e2df2 2002.
> [658746.004124] sd 6:0:2:2: last recovery: 4459793692, now: 4459801236
> [658746.010686] sd 6:0:2:2: [sdk] Result: hostbyte=DID_OK driverbyte=DRIVER_OK,SUGGEST_OK
> [658746.019004] sd 6:0:2:2: [sdk] CDB: Synchronize Cache(10): 35 00 00 00 00 00 00 00 00 00
> [658746.027680] sd 6:0:2:2: Activating scsi error recovery (2)
> [658746.033526] sd 6:0:2:2: trying to abort command
> [658746.038543] qla2xxx 0000:07:02.0: scsi(6:2:2): Abort command issued -- 1 36e2df4 2002.

Does this result in a dead machine, or does the system still struggle
along somehow?

> My guess is that these units flush their cache when this command is send
> even though they have a battery backup unit and flushing 2GB cache may
> take some time... Since I can only reproduce it on systems in production
> I can't do any experiments, but I guess the default timeout of 30s is not
> sufficient.
> 
> Problem is now that this timeout cannot be adjusted by the sysfs scsi device 
> timeout, since sd_prepare_flush() doesn't have the required device 
> structure. The reason for that is blk_queue_ordered(). It neither
> gets a timeout argument, nor any pointer to the device.
> 
> I already tried to use container_of() in sd_prepare_flush, but somehow
> that doesn't seem work if the structure member is a pointer.
> 
> The next solution that comes into my my mind is to add the timeout argument
> to blk_queue_ordered() and subsequentely to modifiy all callers.
> Would such a patch be accepted? Or is there any better solution?
> 
> Any help is appreciated.

Is this problem still open?

> 
> Thanks,
> Bernd
> 
> PS: (I'm also discussing the cache flush issue with one of our 
> hardware vendors, but fixing their firmware might take ages). 

Making the timeout tunable sounds like a suitable (if minimal)
approach.  It appears to presently be a qlogic-specific thing? 
Command_Entry.time_out?
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