linux-kernel - Re: [PATCH -next] block/wbt: fix negative inflight counter when remove scsi device

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Date:   Tue, 14 Dec 2021 09:13:10 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Laibin Qiu <qiulaibin@...wei.com>, axboe@...nel.dk,
        yi.zhang@...wei.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] block/wbt: fix negative inflight counter when
 remove scsi device

On Mon, Dec 13, 2021 at 09:16:51AM -0800, Christoph Hellwig wrote:
> On Mon, Dec 13, 2021 at 12:09:07PM +0800, Laibin Qiu wrote:
> > Submit_bio
> >                                                          scsi_remove_device
> >                                                          sd_remove
> >                                                          del_gendisk
> >                                                          blk_unregister_queue
> >                                                          elv_unregister_queue
> >                                                          wbt_enable_default
> >                                                          <= Set rwb->enable_state (ON)
> > q_qos_track
> > <= rwb->enable_state (ON)
> > ^^^^^^ this request will mark WBT_TRACKED without inflight add and will
> > lead to drop rqw->inflight to -1 in wbt_done() which will trigger IO hung.
> > 
> > Fix this by judge whether QUEUE_FLAG_REGISTERED is marked to distinguish
> > scsi remove scene.
> > Fixes: 76a8040817b4b ("blk-wbt: make sure throttle is enabled properly")
> > Signed-off-by: Laibin Qiu <qiulaibin@...wei.com>
> > ---
> >  block/blk-wbt.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> > index 3ed71b8da887..537f77bb1365 100644
> > --- a/block/blk-wbt.c
> > +++ b/block/blk-wbt.c
> > @@ -637,6 +637,10 @@ void wbt_enable_default(struct request_queue *q)
> >  {
> >  	struct rq_qos *rqos = wbt_rq_qos(q);
> >  
> > +	/* Queue not registered? Maybe shutting down... */
> > +	if (!blk_queue_registered(q))
> > +		return;
> 
> Wouldn't it make more sense to simply not call wbt_enable_default from
> elv_unregister_queue?

wbt_disable_default() is called in bfq_init_root_group(), so wbt_enable_default
should be moved to bfq_exit_queue()?


Thanks,
Ming