On Mon, Jan 21 2019 at 9:46pm -0500, Ming Lei <[email protected]> wrote:
> On Mon, Jan 21, 2019 at 11:02:04AM -0500, Mike Snitzer wrote: > > On Sun, Jan 20 2019 at 10:21P -0500, > > Ming Lei <[email protected]> wrote: > > > > > On Sat, Jan 19, 2019 at 01:05:05PM -0500, Mike Snitzer wrote: > > > > Use the same BIO_QUEUE_ENTERED pattern that was established by commit > > > > cd4a4ae4683dc ("block: don't use blocking queue entered for recursive > > > > bio submits") by setting BIO_QUEUE_ENTERED after bio_split() and before > > > > recursing via generic_make_request(). > > > > > > > > Also add trace_block_split() because it provides useful context about > > > > bio splits in blktrace. > > > > > > > > Depends-on: cd4a4ae4683dc ("block: don't use blocking queue entered for > > > > recursive bio submits") > > > > Fixes: 18a25da84354 ("dm: ensure bio submission follows a depth-first > > > > tree walk") > > > > Cc: [email protected] # 4.16+ > > > > Signed-off-by: Mike Snitzer <[email protected]> > > > > --- > > > > drivers/md/dm.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > > > > index fbadda68e23b..6e29c2d99b99 100644 > > > > --- a/drivers/md/dm.c > > > > +++ b/drivers/md/dm.c > > > > @@ -1654,7 +1654,9 @@ static blk_qc_t __split_and_process_bio(struct > > > > mapped_device *md, > > > > > > > > sectors[op_stat_group(bio_op(bio))], ci.sector_count); > > > > part_stat_unlock(); > > > > > > > > + bio_set_flag(bio, BIO_QUEUE_ENTERED); > > > > bio_chain(b, bio); > > > > + trace_block_split(md->queue, b, > > > > bio->bi_iter.bi_sector); > > > > ret = generic_make_request(bio); > > > > break; > > > > } > > > > > > In theory, BIO_QUEUE_ENTERED is only required when > > > __split_and_process_bio() is > > > called from generic_make_request(). However, it may be called from > > > dm_wq_work(), > > > this way might cause trouble on operation to q->q_usage_counter. > > > > Good point, I've tweaked this patch to clear BIO_QUEUE_ENTERED in > > dm_make_request(). > > > > And to Neil's point: yes, these changes really do need to made > > common since it appears all bio_split() callers do go on to call > > generic_make_request(). > > > > Anyway, here is the updated patch that is now staged in linux-next: > > > > From: Mike Snitzer <[email protected]> > > Date: Fri, 18 Jan 2019 01:21:11 -0500 > > Subject: [PATCH v2] dm: fix missing bio_split() pattern code in > > __split_and_process_bio() > > > > Use the same BIO_QUEUE_ENTERED pattern that was established by commit > > cd4a4ae4683dc ("block: don't use blocking queue entered for recursive > > bio submits") by setting BIO_QUEUE_ENTERED after bio_split() and before > > recursing via generic_make_request(). > > > > Also add trace_block_split() because it provides useful context about > > bio splits in blktrace. > > > > Depends-on: cd4a4ae4683dc ("block: don't use blocking queue entered for > > recursive bio submits") > > Fixes: 18a25da84354 ("dm: ensure bio submission follows a depth-first tree > > walk") > > Cc: [email protected] # 4.16+ > > Signed-off-by: Mike Snitzer <[email protected]> > > --- > > drivers/md/dm.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > > index fbadda68e23b..25884f833a32 100644 > > --- a/drivers/md/dm.c > > +++ b/drivers/md/dm.c > > @@ -1654,7 +1654,9 @@ static blk_qc_t __split_and_process_bio(struct > > mapped_device *md, > > > > sectors[op_stat_group(bio_op(bio))], ci.sector_count); > > part_stat_unlock(); > > > > + bio_set_flag(bio, BIO_QUEUE_ENTERED); > > bio_chain(b, bio); > > + trace_block_split(md->queue, b, > > bio->bi_iter.bi_sector); > > ret = generic_make_request(bio); > > break; > > } > > @@ -1734,6 +1736,13 @@ static blk_qc_t dm_make_request(struct request_queue > > *q, struct bio *bio) > > > > map = dm_get_live_table(md, &srcu_idx); > > > > + /* > > + * Clear the bio-reentered-generic_make_request() flag, > > + * will be set again as needed if bio needs to be split. > > + */ > > + if (bio_flagged(bio, BIO_QUEUE_ENTERED)) > > + bio_clear_flag(bio, BIO_QUEUE_ENTERED); > > + > > /* if we're suspended, we have to queue this io for later */ > > if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) { > > dm_put_live_table(md, srcu_idx); > > -- > > 2.15.0 > > > > Hi Mike, > > I'd suggest to fix this kind issue in the following way, then we > can avoid to touch this flag from drivers: > > diff --git a/block/blk-core.c b/block/blk-core.c > index 3c5f61ceeb67..e70103560ac2 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1024,6 +1024,8 @@ blk_qc_t generic_make_request(struct bio *bio) > else > bio_io_error(bio); > return ret; > + } else { > + bio_set_flag(bio, BIO_QUEUE_ENTERED); > } > > if (!generic_make_request_checks(bio)) > @@ -1074,6 +1076,8 @@ blk_qc_t generic_make_request(struct bio *bio) > if (blk_queue_enter(q, flags) < 0) { > enter_succeeded = false; > q = NULL; > + } else { > + bio_set_flag(bio, BIO_QUEUE_ENTERED); > } > } > > diff --git a/block/blk-merge.c b/block/blk-merge.c > index b990853f6de7..8777e286bd3f 100644 > --- a/block/blk-merge.c > +++ b/block/blk-merge.c > @@ -339,16 +339,6 @@ void blk_queue_split(struct request_queue *q, struct bio > **bio) > /* there isn't chance to merge the splitted bio */ > split->bi_opf |= REQ_NOMERGE; > > - /* > - * Since we're recursing into make_request here, ensure > - * that we mark this bio as already having entered the queue. > - * If not, and the queue is going away, we can get stuck > - * forever on waiting for the queue reference to drop. But > - * that will never happen, as we're already holding a > - * reference to it. > - */ > - bio_set_flag(*bio, BIO_QUEUE_ENTERED); > - > bio_chain(split, *bio); > trace_block_split(q, split, (*bio)->bi_iter.bi_sector); > generic_make_request(*bio); > Not opposed to this. Thanks, Mike
