From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "hch@infradead.org" <hch@infradead.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"tom.leiming@gmail.com" <tom.leiming@gmail.com>,
"axboe@fb.com" <axboe@fb.com>
Cc: "tj@kernel.org" <tj@kernel.org>, "hare@suse.de" <hare@suse.de>
Subject: Re: [PATCH v3 4/4] block: block new I/O just after queue is set as dying
Date: Mon, 27 Mar 2017 15:49:10 +0000 [thread overview]
Message-ID: <1490629737.2461.10.camel@sandisk.com> (raw)
In-Reply-To: <20170327120658.29864-5-tom.leiming@gmail.com>
On Mon, 2017-03-27 at 20:06 +0800, Ming Lei wrote:
> Before commit 780db2071a(blk-mq: decouble blk-mq freezing
> from generic bypassing), the dying flag is checked before
> entering queue, and Tejun converts the checking into .mq_freeze_depth,
> and assumes the counter is increased just after dying flag
> is set. Unfortunately we doesn't do that in blk_set_queue_dying().
>=20
> This patch calls blk_freeze_queue_start() in blk_set_queue_dying(),
> so that we can block new I/O coming once the queue is set as dying.
>=20
> Given blk_set_queue_dying() is always called in remove path
> of block device, and queue will be cleaned up later, we don't
> need to worry about undoing the counter.
>=20
> Cc: Bart Van Assche <bart.vanassche@sandisk.com>
> Cc: Tejun Heo <tj@kernel.org>
> Reviewed-by: Hannes Reinecke <hare@suse.com>
> Signed-off-by: Ming Lei <tom.leiming@gmail.com>
> ---
> block/blk-core.c | 13 ++++++++++---
> 1 file changed, 10 insertions(+), 3 deletions(-)
>=20
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 60f364e1d36b..e22c4ea002ec 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -500,6 +500,13 @@ void blk_set_queue_dying(struct request_queue *q)
> queue_flag_set(QUEUE_FLAG_DYING, q);
> spin_unlock_irq(q->queue_lock);
> =20
> + /*
> + * When queue DYING flag is set, we need to block new req
> + * entering queue, so we call blk_freeze_queue_start() to
> + * prevent I/O from crossing blk_queue_enter().
> + */
> + blk_freeze_queue_start(q);
>
> if (q->mq_ops)
> blk_mq_wake_waiters(q);
> else {
> @@ -672,9 +679,9 @@ int blk_queue_enter(struct request_queue *q, bool now=
ait)
> /*
> * read pair of barrier in blk_freeze_queue_start(),
> * we need to order reading __PERCPU_REF_DEAD flag of
> - * .q_usage_counter and reading .mq_freeze_depth,
> - * otherwise the following wait may never return if the
> - * two reads are reordered.
> + * .q_usage_counter and reading .mq_freeze_depth or
> + * queue dying flag, otherwise the following wait may
> + * never return if the two reads are reordered.
> */
> smp_rmb();
> =20
An explanation of why that crossing can happen is still missing above the
blk_freeze_queue_start() call. Additionally, I'm still wondering whether
or not we need "Cc: stable" tags for the patches in this series. But since
the code looks fine:
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
> =
next prev parent reply other threads:[~2017-03-27 15:49 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-27 12:06 [PATCH v3 0/4] block: misc changes Ming Lei
2017-03-27 12:06 ` [PATCH v3 1/4] blk-mq: comment on races related with timeout handler Ming Lei
2017-03-27 12:11 ` Johannes Thumshirn
2017-03-27 12:06 ` [PATCH v3 2/4] block: add a read barrier in blk_queue_enter() Ming Lei
2017-03-27 12:14 ` Johannes Thumshirn
2017-03-27 15:44 ` Bart Van Assche
2017-03-27 12:06 ` [PATCH v3 3/4] block: rename blk_mq_freeze_queue_start() Ming Lei
2017-03-27 12:15 ` Johannes Thumshirn
2017-03-27 12:06 ` [PATCH v3 4/4] block: block new I/O just after queue is set as dying Ming Lei
2017-03-27 12:16 ` Johannes Thumshirn
2017-03-27 15:49 ` Bart Van Assche [this message]
2017-03-29 2:11 ` [PATCH v3 0/4] block: misc changes Ming Lei
2017-03-29 14:00 ` Jens Axboe
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