[PATCH 5.0 033/139] Revert "MD: fix lock contention for flush bios"

Greg Kroah-Hartman
2019-05-23T19:20:50Z

From: NeilBrown <neilb@suse.com>

commit 4bc034d35377196c854236133b07730a777c4aba upstream.

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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/md.c | 159 +++++++++++++++++++-------------------------------------
drivers/md/md.h | 22 ++-----
2 files changed, 62 insertions(+), 119 deletions(-)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -132,24 +132,6 @@ static inline int speed_max(struct 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
/*
* 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 *mdde
* 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 *mdde
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)
--- 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;