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

[QiuLaibin]

On 2021/12/14 1:16, 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@xxxxxxxxxx>
> > ---
> >   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?
> .

Refer to your opinion, I will post another version of V2.
Please take a look again.