Re: 2.6.24-rc3-mm1

[Jens Axboe <jens.axboe@oracle.com>]

On Wed, Dec 12 2007, Boaz Harrosh wrote:
> On Tue, Dec 11 2007 at 18:33 +0200, James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> > On Mon, 2007-11-26 at 22:15 -0800, Andrew Morton wrote:
> >> OK, thanks.  I'll assume that James and Hannes have this in hand (or will
> >> have, by mid-week) and I won't do anything here.
> > 
> > Just to confirm what I think I'm going to be doing:  rebasing the
> > scsi-misc tree to remove this commit:
> > 
> > commit 8655a546c83fc43f0a73416bbd126d02de7ad6c0
> > Author: Hannes Reinecke <hare@suse.de>
> > Date:   Tue Nov 6 09:23:40 2007 +0100
> > 
> >     [SCSI] Do not requeue requests if REQ_FAILFAST is set
> > 
> > And its allied fix ups:
> > 
> > commit 983289045faa96fba8841d3c51b98bb8623d9504
> > Author: James Bottomley <James.Bottomley@HansenPartnership.com>
> > Date:   Sat Nov 24 19:47:25 2007 +0200
> > 
> >     [SCSI] fix up REQ_FASTFAIL not to fail when state is QUIESCE
> > 
> > commit 9dd15a13b332e9f5c8ee752b1ccd9b84cb5bdf17
> > Author: James Bottomley <James.Bottomley@HansenPartnership.com>
> > Date:   Sat Nov 24 19:55:53 2007 +0200
> > 
> >     [SCSI] fix domain validation to work again
> > 
> > James
> > 
> 
> The problems caused by this patch where nagging me at the back of my head
> from the begging. Why should we fail on a check of FAIL_FAST in all kind
> of weird places like boots, when the only place that should ever set the 
> flag should be one of the multi-path drivers. finally it struck me:
> 
> It might be a bug in ll_rw_blk at blk_rq_bio_prep() there is this:
> 
> static void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
> 			    struct bio *bio)
> {
> 	/* first two bits are identical in rq->cmd_flags and bio->bi_rw */
> 	rq->cmd_flags |= (bio->bi_rw & 3);
> 	...
> 
> Now this is no longer true and is a bug.
> Second bit of bio->bi_rw defined in bio.h is:
> #define BIO_RW_AHEAD	1
> but
> Second bit of rq->cmd_flags is __REQ_FAILFAST
> 
> so maybe we are getting FAILFAST in the wrong places?

But that's actually on purpose, though the comment is pretty much crap.
We don't want to be retrying readahead requests, those should always
just be tossable.

-- 
Jens Axboe