linux-kernel - Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with sequenced flush

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Message-ID: <4C73FD52.7000305@vlnb.net>
Date:	Tue, 24 Aug 2010 21:11:46 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Tejun Heo <tj@...nel.org>
CC:	Kiyoshi Ueda <k-ueda@...jp.nec.com>,
	Christoph Hellwig <hch@....de>, jaxboe@...ionio.com,
	linux-fsdevel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-raid@...r.kernel.org, James.Bottomley@...e.de, tytso@....edu,
	chris.mason@...cle.com, swhiteho@...hat.com,
	konishi.ryusuke@....ntt.co.jp, dm-devel@...hat.com, jack@...e.cz,
	rwheeler@...hat.com, hare@...e.de
Subject: Re: [PATCHSET block#for-2.6.36-post] block: replace barrier with
 sequenced flush

Tejun Heo, on 08/23/2010 04:14 PM wrote:
>> I think that's correct and changing the priority of DM_ENDIO_REQUEUE
>> for REQ_FLUSH down to the lowest should be fine.
>> (I didn't know that FLUSH failure implies data loss possibility.)
>
> At least on ATA, FLUSH failure implies that data is already lost, so
> the error can't be ignored or retried.

In SCSI there are conditions when a command, including FLUSH 
(SYNC_CACHE), failed which don't imply lost data. For them the caller 
expected to retry the failed command. Most common cases are Unit 
Attentions and TASK QUEUE FULL status.

Vlad
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