linux-kernel - Re: [PATCH v1 3/3] blk-mq: start to freeze queue just after setting dying

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Date:   Sat, 18 Mar 2017 12:27:33 +0100
From:   Hannes Reinecke <hare@...e.de>
To:     Ming Lei <tom.leiming@...il.com>, Jens Axboe <axboe@...com>,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>
Cc:     Yi Zhang <yizhan@...hat.com>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v1 3/3] blk-mq: start to freeze queue just after setting
 dying

On 03/17/2017 10:57 AM, 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().
> 
> This patch calls blk_mq_freeze_queue_start() for blk-mq in
> blk_set_queue_dying(), so that we can block new I/O coming
> once the queue is set as dying.
> 
> 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.
> 
> Cc: Bart Van Assche <bart.vanassche@...disk.com>
> Cc: Tejun Heo <tj@...nel.org>
> Signed-off-by: Ming Lei <tom.leiming@...il.com>
> ---
>  block/blk-core.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@...e.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)