Re: [PATCH v2 1/4] blk-flush: flush_rq should inherit first_rq's cmd_flags

[Hannes Reinecke]

On 7/31/23 08:09, Christoph Hellwig wrote:
> On Tue, Jul 25, 2023 at 09:00:59PM +0800, chengming.zhou@xxxxxxxxx wrote:
> > From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> >
> > 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
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