From: Jens Axboe <jens.axboe@oracle.com>
To: Daniel Phillips <phillips@phunq.net>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC] [PATCH] A clean aEvgeniy pproach to writeout throttling
Date: Mon, 10 Dec 2007 12:41:23 +0100 [thread overview]
Message-ID: <20071210114123.GE5008@kernel.dk> (raw)
In-Reply-To: <200712100323.48535.phillips@phunq.net>
On Mon, Dec 10 2007, Daniel Phillips wrote:
> On Monday 10 December 2007 02:47, Jens Axboe wrote:
> > Ehm, this patch is so broken it's not even funny - did you even
> > compile? You would have noticed the warning on request_queue_t,
> > surely. The big problem is the last hunk here though, how would that
> > work on stacked devices? Clue: ->bi_bdev is not const, it can change
> > after a call to ->make_request_fn().
>
> Such paranoia. Yes, the patch was compiled. Yes, the warning was
> slipped through. No, it is not substantive, and in fact was removed
> from another branch of our tree already.
>
> Ignoring the rhetoric, apparently you missed the line:
>
> + if (q && q->metric && !bio->bi_queue) {
>
> The prevents any reference ti bi_bdev after the intial call to
> generic_make_request. Thanks to Evgeniy for pointing out the need for
> this measure on the last go round.
Which saves the initial target, for ease of accounting at end io time -
that's not the point. What happens when ->make_request_fn() changes
bio->bi_bdev and returns 1, causing another iteration of the
__generic_make_request() loop? 'q' is no longer the valid target,
bdev_get_queue(bio->bi_bdev) is.
> "So broken" is a gross exaggeration. Substantive comments welcome.
Or you could try and make an effort to understand the comment instead of
just glancing over it.
--
Jens Axboe
next prev parent reply other threads:[~2007-12-10 11:44 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-12-06 0:03 [RFC] [PATCH] A clean approach to writeout throttling Daniel Phillips
2007-12-06 1:24 ` Andrew Morton
2007-12-06 6:21 ` Daniel Phillips
2007-12-06 7:31 ` Andrew Morton
2007-12-06 9:48 ` Daniel Phillips
2007-12-06 11:55 ` Andrew Morton
2007-12-06 15:52 ` Rik van Riel
2007-12-06 17:34 ` Andrew Morton
2007-12-06 17:48 ` Rik van Riel
2007-12-06 20:04 ` Daniel Phillips
2007-12-06 20:27 ` Andrew Morton
2007-12-06 21:27 ` Daniel Phillips
2007-12-06 21:53 ` Bill Davidsen
2007-12-07 0:04 ` Daniel Phillips
2007-12-07 0:29 ` Andrew Morton
2007-12-07 7:13 ` Daniel Phillips
2007-12-10 9:20 ` Daniel Phillips
2007-12-10 10:47 ` Jens Axboe
2007-12-10 11:23 ` [RFC] [PATCH] A clean aEvgeniy pproach " Daniel Phillips
2007-12-10 11:41 ` Jens Axboe [this message]
2007-12-10 12:13 ` Daniel Phillips
2007-12-10 12:16 ` Jens Axboe
2007-12-10 12:27 ` Daniel Phillips
2007-12-10 12:32 ` Jens Axboe
2007-12-10 13:04 ` Daniel Phillips
2007-12-10 13:19 ` Jens Axboe
2007-12-10 13:26 ` Daniel Phillips
2007-12-10 13:30 ` Jens Axboe
2007-12-10 13:43 ` Daniel Phillips
2007-12-10 13:53 ` Jens Axboe
2007-12-10 14:17 ` Daniel Phillips
2007-12-11 13:15 ` Jens Axboe
2007-12-11 19:38 ` Daniel Phillips
2007-12-11 20:01 ` Jens Axboe
2007-12-11 20:11 ` Daniel Phillips
2007-12-11 20:07 ` Daniel Phillips
2007-12-10 11:33 ` [RFC] [PATCH] A clean approach " Daniel Phillips
2007-12-10 21:31 ` Jonathan Corbet
2007-12-10 22:06 ` Pekka Enberg
2007-12-11 4:21 ` Daniel Phillips
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