From: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
To: zaitcev@redhat.com
Cc: jens.axboe@oracle.com, linux-kernel@vger.kernel.org,
linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org,
dm-devel@redhat.com, j-nomura@ce.jp.nec.com,
k-ueda@ct.jp.nec.com
Subject: Re: [PATCH 12/30] blk_end_request: changing ub (take 4)
Date: Wed, 12 Dec 2007 15:38:15 -0500 (EST) [thread overview]
Message-ID: <20071212.153815.39152138.k-ueda@ct.jp.nec.com> (raw)
In-Reply-To: <20071211154803.58beb681.zaitcev@redhat.com>
Hi Pete,
On Tue, 11 Dec 2007 15:48:03 -0800, Pete Zaitcev <zaitcev@redhat.com> wrote:
> > if (scsi_status == 0) {
> > - uptodate = 1;
> > + error = 0;
> > } else {
> > - uptodate = 0;
> > + error = -EIO;
> > rq->errors = scsi_status;
> > }
> > - end_that_request_first(rq, uptodate, rq->hard_nr_sectors);
> > - end_that_request_last(rq, uptodate);
> > + if (__blk_end_request(rq, error, blk_rq_bytes(rq)))
> > + BUG();
>
> Acked-by: Pete Zaitcev <zaitcev@redhat.com>
>
> I follow the discussion, actually, and wanted to ask someone to look
> closer if it's appropriate to use __blk_end_request() here.
> My understanding was, blk_end_request() is the same thing, only
> takes the queue lock. But then, should I refactor ub so that it
> calls __blk_end_request if request function ends with an error
> and blk_end_request if the end-of-IO even is processed? If not,
> and the above is sufficient, why have blk_end_request at all?
The difference between blk_end_request() and __blk_end_request() is
whether the queue lock is held or not when end_that_request_last()
is called.
It's not relevant to the status of the request (error or not).
I'm using __blk_end_request() here and I think it's sufficient, because:
o end_that_request_last() must be called with the queue lock held
o ub_end_rq() calls end_that_request_last() without taking
the queue lock in itself.
So the queue lock must have been taken outside ub_end_rq().
But, if ub is calling end_that_request_last() without the queue lock,
it is a bug in the original code and we should use blk_end_request()
to fix that.
Does that answer satisfy you?
Thanks,
Kiyoshi Ueda
next prev parent reply other threads:[~2007-12-12 20:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-11 22:46 [PATCH 12/30] blk_end_request: changing ub (take 4) Kiyoshi Ueda
2007-12-11 23:48 ` Pete Zaitcev
2007-12-12 20:38 ` Kiyoshi Ueda [this message]
2007-12-13 21:59 ` Pete Zaitcev
2007-12-14 17:04 ` Kiyoshi Ueda
2007-12-14 19:49 ` Pete Zaitcev
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