From: NeilBrown neilb@suse.com

This reverts commit 5a409b4f56d50b212334f338cb8465d65550cd85.

This patch has two problems.

1/ it make multiple calls to submit_bio() from inside a make_request_fn. The bios thus submitted will be queued on current->bio_list and not submitted immediately. As the bios are allocated from a mempool, this can theoretically result in a deadlock - all the pool of requests could be in various ->bio_list queues and a subsequent mempool_alloc could block waiting for one of them to be released.

2/ It aims to handle a case when there are many concurrent flush requests. It handles this by submitting many requests in parallel - all of which are identical and so most of which do nothing useful. It would be more efficient to just send one lower-level request, but allow that to satisfy multiple upper-level requests.

Fixes: 5a409b4f56d5 ("MD: fix lock contention for flush bios") Cc: stable@vger.kernel.org # v4.19+ Tested-by: Xiao Ni xni@redhat.com Signed-off-by: NeilBrown neilb@suse.com Signed-off-by: Song Liu songliubraving@fb.com --- drivers/md/md.c | 159 +++++++++++++++++------------------------------- drivers/md/md.h | 22 +++---- 2 files changed, 62 insertions(+), 119 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c index 05ffffb8b769..021e522001c1 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -132,24 +132,6 @@ static inline int speed_max(struct mddev *mddev) mddev->sync_speed_max : sysctl_speed_limit_max; }

-static void * flush_info_alloc(gfp_t gfp_flags, void *data) -{ - return kzalloc(sizeof(struct flush_info), gfp_flags); -} -static void flush_info_free(void *flush_info, void *data) -{ - kfree(flush_info); -} - -static void * flush_bio_alloc(gfp_t gfp_flags, void *data) -{ - return kzalloc(sizeof(struct flush_bio), gfp_flags); -} -static void flush_bio_free(void *flush_bio, void *data) -{ - kfree(flush_bio); -} - static struct ctl_table_header *raid_table_header;

static struct ctl_table raid_table[] = { @@ -423,54 +405,30 @@ static int md_congested(void *data, int bits) /* * Generic flush handling for md */ -static void submit_flushes(struct work_struct *ws) -{ - struct flush_info *fi = container_of(ws, struct flush_info, flush_work); - struct mddev *mddev = fi->mddev; - struct bio *bio = fi->bio; - - bio->bi_opf &= ~REQ_PREFLUSH; - md_handle_request(mddev, bio); - - mempool_free(fi, mddev->flush_pool); -}

-static void md_end_flush(struct bio *fbio) +static void md_end_flush(struct bio *bio) { - struct flush_bio *fb = fbio->bi_private; - struct md_rdev *rdev = fb->rdev; - struct flush_info *fi = fb->fi; - struct bio *bio = fi->bio; - struct mddev *mddev = fi->mddev; + struct md_rdev *rdev = bio->bi_private; + struct mddev *mddev = rdev->mddev;

rdev_dec_pending(rdev, mddev);

- if (atomic_dec_and_test(&fi->flush_pending)) { - if (bio->bi_iter.bi_size == 0) { - /* an empty barrier - all done */ - bio_endio(bio); - mempool_free(fi, mddev->flush_pool); - } else { - INIT_WORK(&fi->flush_work, submit_flushes); - queue_work(md_wq, &fi->flush_work); - } + if (atomic_dec_and_test(&mddev->flush_pending)) { + /* The pre-request flush has finished */ + queue_work(md_wq, &mddev->flush_work); } - - mempool_free(fb, mddev->flush_bio_pool); - bio_put(fbio); + bio_put(bio); }

-void md_flush_request(struct mddev *mddev, struct bio *bio) +static void md_submit_flush_data(struct work_struct *ws); + +static void submit_flushes(struct work_struct *ws) { + struct mddev *mddev = container_of(ws, struct mddev, flush_work); struct md_rdev *rdev; - struct flush_info *fi; - - fi = mempool_alloc(mddev->flush_pool, GFP_NOIO); - - fi->bio = bio; - fi->mddev = mddev; - atomic_set(&fi->flush_pending, 1);

+ INIT_WORK(&mddev->flush_work, md_submit_flush_data); + atomic_set(&mddev->flush_pending, 1); rcu_read_lock(); rdev_for_each_rcu(rdev, mddev) if (rdev->raid_disk >= 0 && @@ -480,40 +438,59 @@ void md_flush_request(struct mddev *mddev, struct bio *bio) * we reclaim rcu_read_lock */ struct bio *bi; - struct flush_bio *fb; atomic_inc(&rdev->nr_pending); atomic_inc(&rdev->nr_pending); rcu_read_unlock(); - - fb = mempool_alloc(mddev->flush_bio_pool, GFP_NOIO); - fb->fi = fi; - fb->rdev = rdev; - bi = bio_alloc_mddev(GFP_NOIO, 0, mddev); - bio_set_dev(bi, rdev->bdev); bi->bi_end_io = md_end_flush; - bi->bi_private = fb; + bi->bi_private = rdev; + bio_set_dev(bi, rdev->bdev); bi->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH; - - atomic_inc(&fi->flush_pending); + atomic_inc(&mddev->flush_pending); submit_bio(bi); - rcu_read_lock(); rdev_dec_pending(rdev, mddev); } rcu_read_unlock(); + if (atomic_dec_and_test(&mddev->flush_pending)) + queue_work(md_wq, &mddev->flush_work); +}

- if (atomic_dec_and_test(&fi->flush_pending)) { - if (bio->bi_iter.bi_size == 0) { - /* an empty barrier - all done */ - bio_endio(bio); - mempool_free(fi, mddev->flush_pool); - } else { - INIT_WORK(&fi->flush_work, submit_flushes); - queue_work(md_wq, &fi->flush_work); - } +static void md_submit_flush_data(struct work_struct *ws) +{ + struct mddev *mddev = container_of(ws, struct mddev, flush_work); + struct bio *bio = mddev->flush_bio; + + /* + * must reset flush_bio before calling into md_handle_request to avoid a + * deadlock, because other bios passed md_handle_request suspend check + * could wait for this and below md_handle_request could wait for those + * bios because of suspend check + */ + mddev->flush_bio = NULL; + wake_up(&mddev->sb_wait); + + if (bio->bi_iter.bi_size == 0) { + /* an empty barrier - all done */ + bio_endio(bio); + } else { + bio->bi_opf &= ~REQ_PREFLUSH; + md_handle_request(mddev, bio); } } + +void md_flush_request(struct mddev *mddev, struct bio *bio) +{ + spin_lock_irq(&mddev->lock); + wait_event_lock_irq(mddev->sb_wait, + !mddev->flush_bio, + mddev->lock); + mddev->flush_bio = bio; + spin_unlock_irq(&mddev->lock); + + INIT_WORK(&mddev->flush_work, submit_flushes); + queue_work(md_wq, &mddev->flush_work); +} EXPORT_SYMBOL(md_flush_request);

static inline struct mddev *mddev_get(struct mddev *mddev) @@ -560,6 +537,7 @@ void mddev_init(struct mddev *mddev) atomic_set(&mddev->openers, 0); atomic_set(&mddev->active_io, 0); spin_lock_init(&mddev->lock); + atomic_set(&mddev->flush_pending, 0); init_waitqueue_head(&mddev->sb_wait); init_waitqueue_head(&mddev->recovery_wait); mddev->reshape_position = MaxSector; @@ -5511,22 +5489,6 @@ int md_run(struct mddev *mddev) if (err) return err; } - if (mddev->flush_pool == NULL) { - mddev->flush_pool = mempool_create(NR_FLUSH_INFOS, flush_info_alloc, - flush_info_free, mddev); - if (!mddev->flush_pool) { - err = -ENOMEM; - goto abort; - } - } - if (mddev->flush_bio_pool == NULL) { - mddev->flush_bio_pool = mempool_create(NR_FLUSH_BIOS, flush_bio_alloc, - flush_bio_free, mddev); - if (!mddev->flush_bio_pool) { - err = -ENOMEM; - goto abort; - } - }

spin_lock(&pers_lock); pers = find_pers(mddev->level, mddev->clevel); @@ -5686,11 +5648,8 @@ int md_run(struct mddev *mddev) return 0;

abort: - mempool_destroy(mddev->flush_bio_pool); - mddev->flush_bio_pool = NULL; - mempool_destroy(mddev->flush_pool); - mddev->flush_pool = NULL; - + bioset_exit(&mddev->bio_set); + bioset_exit(&mddev->sync_set); return err; } EXPORT_SYMBOL_GPL(md_run); @@ -5894,14 +5853,6 @@ static void __md_stop(struct mddev *mddev) mddev->to_remove = &md_redundancy_group; module_put(pers->owner); clear_bit(MD_RECOVERY_FROZEN, &mddev->recovery); - if (mddev->flush_bio_pool) { - mempool_destroy(mddev->flush_bio_pool); - mddev->flush_bio_pool = NULL; - } - if (mddev->flush_pool) { - mempool_destroy(mddev->flush_pool); - mddev->flush_pool = NULL; - } }

void md_stop(struct mddev *mddev) diff --git a/drivers/md/md.h b/drivers/md/md.h index c52afb52c776..2deb84fa93f9 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -252,19 +252,6 @@ enum mddev_sb_flags { MD_SB_NEED_REWRITE, /* metadata write needs to be repeated */ };

-#define NR_FLUSH_INFOS 8 -#define NR_FLUSH_BIOS 64 -struct flush_info { - struct bio *bio; - struct mddev *mddev; - struct work_struct flush_work; - atomic_t flush_pending; -}; -struct flush_bio { - struct flush_info *fi; - struct md_rdev *rdev; -}; - struct mddev { void *private; struct md_personality *pers; @@ -470,8 +457,13 @@ struct mddev { * metadata and bitmap writes */

- mempool_t *flush_pool; - mempool_t *flush_bio_pool; + /* Generic flush handling. + * The last to finish preflush schedules a worker to submit + * the rest of the request (without the REQ_PREFLUSH flag). + */ + struct bio *flush_bio; + atomic_t flush_pending; + struct work_struct flush_work; struct work_struct event_work; /* used by dm to report failure event */ void (*sync_super)(struct mddev *mddev, struct md_rdev *rdev); struct md_cluster_info *cluster_info;