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From: Mike Snitzer <snitzer@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, dm-devel@redhat.com,
	Uday Shankar <ushankar@purestorage.com>,
	Alasdair Kergon <agk@redhat.com>
Subject: Re: [dm-devel] blk-mq: enforce op-specific segment limits in blk_insert_cloned_request
Date: Fri, 17 Feb 2023 11:43:34 -0500	[thread overview]
Message-ID: <Y++utrkJXuUsD0K4@redhat.com> (raw)
In-Reply-To: <Y++oTz0ck9OGE4Se@infradead.org>

On Fri, Feb 17 2023 at 11:16P -0500,
Christoph Hellwig <hch@infradead.org> wrote:

> On Thu, Feb 16, 2023 at 12:27:02PM -0700, Uday Shankar wrote:
> >  * Description:
> >  *    @rq may have been made based on weaker limitations of upper-level queues
> >  *    in request stacking drivers, and it may violate the limitation of @q.
> >  *    Since the block layer and the underlying device driver trust @rq
> >  *    after it is inserted to @q, it should be checked against @q before
> >  *    the insertion using this generic function.
> >  *
> >  *    Request stacking drivers like request-based dm may change the queue
> >  *    limits when retrying requests on other queues. Those requests need
> >  *    to be checked against the new queue limits again during dispatch.
> >  */.
> > 
> > Is this concern no longer relevant?
> 
> The concern is still valid, but it does not refer to the debug check.
> It refers to recalculating nr_phys_segments using
> blk_recalc_rq_segments, and the fact that any driver using this
> interface needs to stack its limits properly.

It is a negative check that you're calling a debug check.

Much easier to address a bug in a driver when seeing this message than
figuring it out after more elaborate hunting. Not seeing the downside
of preserving/fixing given it is a quick limit check. *shrug*

--
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https://listman.redhat.com/mailman/listinfo/dm-devel


WARNING: multiple messages have this Message-ID (diff)
From: Mike Snitzer <snitzer@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Uday Shankar <ushankar@purestorage.com>,
	Jens Axboe <axboe@kernel.dk>, Alasdair Kergon <agk@redhat.com>,
	linux-block@vger.kernel.org, dm-devel@redhat.com
Subject: Re: blk-mq: enforce op-specific segment limits in blk_insert_cloned_request
Date: Fri, 17 Feb 2023 11:43:34 -0500	[thread overview]
Message-ID: <Y++utrkJXuUsD0K4@redhat.com> (raw)
In-Reply-To: <Y++oTz0ck9OGE4Se@infradead.org>

On Fri, Feb 17 2023 at 11:16P -0500,
Christoph Hellwig <hch@infradead.org> wrote:

> On Thu, Feb 16, 2023 at 12:27:02PM -0700, Uday Shankar wrote:
> >  * Description:
> >  *    @rq may have been made based on weaker limitations of upper-level queues
> >  *    in request stacking drivers, and it may violate the limitation of @q.
> >  *    Since the block layer and the underlying device driver trust @rq
> >  *    after it is inserted to @q, it should be checked against @q before
> >  *    the insertion using this generic function.
> >  *
> >  *    Request stacking drivers like request-based dm may change the queue
> >  *    limits when retrying requests on other queues. Those requests need
> >  *    to be checked against the new queue limits again during dispatch.
> >  */.
> > 
> > Is this concern no longer relevant?
> 
> The concern is still valid, but it does not refer to the debug check.
> It refers to recalculating nr_phys_segments using
> blk_recalc_rq_segments, and the fact that any driver using this
> interface needs to stack its limits properly.

It is a negative check that you're calling a debug check.

Much easier to address a bug in a driver when seeing this message than
figuring it out after more elaborate hunting. Not seeing the downside
of preserving/fixing given it is a quick limit check. *shrug*

  reply	other threads:[~2023-02-17 16:43 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-15 20:15 [dm-devel] [PATCH] blk-mq: enforce op-specific segment limits in blk_insert_cloned_request Uday Shankar
2023-02-15 20:15 ` Uday Shankar
2023-02-16  6:09 ` [dm-devel] " Christoph Hellwig
2023-02-16  6:09   ` Christoph Hellwig
2023-02-16 19:27   ` [dm-devel] " Uday Shankar
2023-02-16 19:27     ` Uday Shankar
2023-02-17  0:13     ` [dm-devel] " Mike Snitzer
2023-02-17  0:13       ` Mike Snitzer
2023-02-17 16:16     ` [dm-devel] [PATCH] " Christoph Hellwig
2023-02-17 16:16       ` Christoph Hellwig
2023-02-17 16:43       ` Mike Snitzer [this message]
2023-02-17 16:43         ` Mike Snitzer
2023-02-17 21:41         ` [dm-devel] " Uday Shankar
2023-02-17 21:41           ` Uday Shankar
2023-02-16 13:06 ` [dm-devel] [PATCH] " kernel test robot
2023-02-16 13:06   ` kernel test robot

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