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Message-ID: <de6ba52c-0f14-670f-7262-93f2aced926a@suse.de>
Date:   Mon, 31 Jul 2023 18:28:01 +0200
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Subject: Re: [PATCH v2 1/4] blk-flush: flush_rq should inherit first_rq's
 cmd_flags
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To:     Christoph Hellwig <hch@lst.de>, chengming.zhou@linux.dev
Cc:     axboe@kernel.dk, ming.lei@redhat.com, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, zhouchengming@bytedance.com
References: <20230725130102.3030032-1-chengming.zhou@linux.dev>
 <20230725130102.3030032-2-chengming.zhou@linux.dev>
 <20230731060957.GA30409@lst.de>
From:   Hannes Reinecke <hare@suse.de>
In-Reply-To: <20230731060957.GA30409@lst.de>
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On 7/31/23 08:09, Christoph Hellwig wrote:
> On Tue, Jul 25, 2023 at 09:00:59PM +0800, chengming.zhou@linux.dev wrote:
>> From: Chengming Zhou <zhouchengming@bytedance.com>
>>
>> The cmd_flags in blk_kick_flush() should inherit the original request's
>> cmd_flags, but the current code looks buggy to me:
> 
> Should it?  I know the code is kinda trying to do it, but does it really
> make sense?  Adding Hannes who originally added this inheritance and
> discussing the details below:
> 
Yeah, it does.
The flush machinery is sending flushes before and/or after the original 
request (preflush/postflush). For blocked transports (ie during FC RSCN 
handling) the transport will error out commands depending on the 
FAILFAST setting. If FAILFAST is set the SCSI layer gets an 
STS_TRANSPORT error (causing the I/O to be retried), but STS_ERROR if 
not set (causing I/O to failed).

So if the FAILFAST setting is _not_ aligned between flush_rq and the 
original we'll get an error on the flush rq and a retry on the original 
rq, causing the entire command to fail.

I guess we need to align them.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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