Re: [PATCH 4/5] block: move queue enter logic into blk_mq_submit_bio()

[Ming Lei <ming.lei@redhat.com>]

On Thu, Nov 11, 2021 at 03:17:27PM -0700, Jens Axboe wrote:
> On 11/11/21 8:23 AM, Ming Lei wrote:
> > Hi Geert,
> > 
> > On Thu, Nov 11, 2021 at 03:51:28PM +0100, Geert Uytterhoeven wrote:
> >> Hi Ming,
> >>
> >> On Thu, Nov 11, 2021 at 2:45 PM Ming Lei <ming.lei@redhat.com> wrote:
> >>> On Thu, Nov 11, 2021 at 01:58:38PM +0100, Geert Uytterhoeven wrote:
> >>>> On Thu, 4 Nov 2021, Jens Axboe wrote:
> >>>>> On 11/4/21 1:04 PM, Christoph Hellwig wrote:
> >>>>>> On Thu, Nov 04, 2021 at 01:02:54PM -0600, Jens Axboe wrote:
> >>>>>>> On 11/4/21 12:52 PM, Christoph Hellwig wrote:
> >>>>>>>> Looks good:
> >>>>>>>>
> >>>>>>>> Reviewed-by: Christoph Hellwig <hch@lst.de>
> >>>>>>>
> >>>>>>> So these two are now:
> >>>>>>>
> >>>>>>> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.16/block&id=c98cb5bbdab10d187aff9b4e386210eb2332af96
> >>>>>>>
> >>>>>>> which is the one I sent here, and then the next one gets cleaned up to
> >>>>>>> remove that queue enter helper:
> >>>>>>>
> >>>>>>> https://git.kernel.dk/cgit/linux-block/commit/?h=for-5.16/block&id=7f930eb31eeb07f1b606b3316d8ad3ab6a92905b
> >>>>>>>
> >>>>>>> Can I add your reviewed-by to this last one as well? Only change is the
> >>>>>>> removal of blk_mq_enter_queue() and the weird construct there, it's just
> >>>>>>> bio_queue_enter() now.
> >>>>>>
> >>>>>> Sure.
> >>>>>
> >>>>> Thanks, prematurely already done, as you could tell :-)
> >>>>
> >>>> The updated version is now commit 900e080752025f00 ("block: move queue
> >>>> enter logic into blk_mq_submit_bio()") in Linus' tree.
> >>>>
> >>>> I have bisected failures on m68k/atari (on ARAnyM, using nfhd as the
> >>>> root device) to this commit, e.g.:
> >>>>
> >>>>     sd 0:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> >>>>     sd 0:0:0:0: [sda] tag#0 Sense Key : Illegal Request [current]
> >>>>     sd 0:0:0:0: [sda] tag#0 Add. Sense: Invalid field in cdb
> >>>>     sd 0:0:0:0: [sda] tag#0 CDB: Write(10) 2a 08 00 00 00 01 00 00 08 00
> >>>>     critical target error, dev sda, sector 1 op 0x1:(WRITE) flags 0x20800 phys_seg 1 prio class 0
> >>>>     Buffer I/O error on dev sda1, logical block 0, lost sync page write
> >>>>
> >>>>     EXT4-fs (sda1): I/O error while writing superblock
> >>>>     sd 0:0:0:0: [sda] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_OK cmd_age=0s
> >>>>     sd 0:0:0:0: [sda] tag#0 Sense Key : Illegal Request [current]
> >>>>     sd 0:0:0:0: [sda] tag#0 Add. Sense: Invalid field in cdb
> >>>>     sd 0:0:0:0: [sda] tag#0 CDB: Write(10) 2a 08 00 00 00 01 00 00 08 00
> >>>>     critical target error, dev sda, sector 1 op 0x1:(WRITE) flags 0x20800 phys_seg 1 prio class 0
> >>>>     Buffer I/O error on dev sda1, logical block 0, lost sync page write
> >>>>     EXT4-fs (sda1): I/O error while writing superblock
> >>>>
> >>>> This may happen either when mounting the root file system (leading to an
> >>>> unable to mount root fs panic), or later (leading to a read-only
> >>>> rootfs).
> >>>
> >>> BTW, today I just found that hang in blk_mq_freeze_queue_wait() is
> >>> caused by commit 900e080752025f00, and the following patch can fix it:
> >>>
> >>> - blk-mq: don't grab ->q_usage_counter in blk_mq_sched_bio_merge
> >>>
> >>> https://lore.kernel.org/linux-block/20211111085650.GA476@lst.de/T/#m759b88fda094a65ebf29bc81b780967cdaf9cf28
> >>>
> >>> Maybe you can try the above patch.
> >>
> >> Thanks! I have applied both patches, but it doesn't make a difference.
> > 
> > Thanks for your test!
> > 
> > Can you try the following patch?
> > 
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index f511db395c7f..a5ab2f2e9f67 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2517,7 +2517,6 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
> >  	struct blk_mq_alloc_data data = {
> >  		.q		= q,
> >  		.nr_tags	= 1,
> > -		.cmd_flags	= bio->bi_opf,
> >  	};
> >  	struct request *rq;
> >  
> > @@ -2525,6 +2524,7 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
> >  		return NULL;
> >  	if (unlikely(!submit_bio_checks(bio)))
> >  		goto put_exit;
> > +	data.cmd_flags	= bio->bi_opf;
> >  	if (blk_mq_attempt_bio_merge(q, bio, nsegs, same_queue_rq))
> >  		goto put_exit;
> 
> That's definitely a real fix, akin to the other pre-enter variants, this
> one just post checks. Geert, can you give this a whirl?
> 
> Ming, would you mind sending this as a real patch?

Hi Jens,

The above patch may not be enough, since submit_bio_checks() is done in
case of using cached request, so how about the following patch(un-tested)?


diff --git a/block/blk-mq.c b/block/blk-mq.c
index f511db395c7f..f84044c8de3f 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2517,7 +2517,6 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
 	struct blk_mq_alloc_data data = {
 		.q		= q,
 		.nr_tags	= 1,
-		.cmd_flags	= bio->bi_opf,
 	};
 	struct request *rq;
 
@@ -2525,6 +2524,7 @@ static struct request *blk_mq_get_new_requests(struct request_queue *q,
 		return NULL;
 	if (unlikely(!submit_bio_checks(bio)))
 		goto put_exit;
+	data.cmd_flags	= bio->bi_opf;
 	if (blk_mq_attempt_bio_merge(q, bio, nsegs, same_queue_rq))
 		goto put_exit;
 
@@ -2564,13 +2564,15 @@ static inline struct request *blk_mq_get_request(struct request_queue *q,
 			if (blk_mq_attempt_bio_merge(q, bio, nsegs,
 						same_queue_rq))
 				return NULL;
+			if (bio->bi_opf != rq->cmd_flags)
+				goto fallback;
 			plug->cached_rq = rq_list_next(rq);
 			INIT_LIST_HEAD(&rq->queuelist);
 			rq_qos_throttle(q, bio);
 			return rq;
 		}
 	}
-
+fallback:
 	return blk_mq_get_new_requests(q, plug, bio, nsegs, same_queue_rq);
 }
 

-- 
Ming