Merge branch 'md-next' of...

Merge branch 'md-next' of https://git.kernel.org/pub/scm/linux/kernel/git/song/md into for-5.14/drivers

Pull MD changes from Song:

"1) iostats rewrite by Guoqing Jiang;
 2) raid5 lock contention optimization by Gal Ofri."

* 'md-next' of https://git.kernel.org/pub/scm/linux/kernel/git/song/md:
  md/raid5: avoid device_lock in read_one_chunk()
  md: add comments in md_integrity_register
  md: check level before create and exit io_acct_set
  md: Constify attribute_group structs
  md: mark some personalities as deprecated
  md/raid10: enable io accounting
  md/raid1: enable io accounting
  md/raid1: rename print_msg with r1bio_existed
  md/raid5: avoid redundant bio clone in raid5_read_one_chunk
  md/raid5: move checking badblock before clone bio in raid5_read_one_chunk
  md: add io accounting for raid0 and raid5
  md: revert io stats accounting

drivers/md/Kconfig

@@ -47,7 +47,7 @@ config MD_AUTODETECT
 	  If unsure, say Y.
 
 config MD_LINEAR
-	tristate "Linear (append) mode"
+	tristate "Linear (append) mode (deprecated)"
 	depends on BLK_DEV_MD
 	help
 	  If you say Y here, then your multiple devices driver will be able to
@@ -158,7 +158,7 @@ config MD_RAID456
 	  If unsure, say Y.
 
 config MD_MULTIPATH
-	tristate "Multipath I/O support"
+	tristate "Multipath I/O support (deprecated)"
 	depends on BLK_DEV_MD
 	help
 	  MD_MULTIPATH provides a simple multi-path personality for use
@@ -169,7 +169,7 @@ config MD_MULTIPATH
 	  If unsure, say N.
 
 config MD_FAULTY
-	tristate "Faulty test module for MD"
+	tristate "Faulty test module for MD (deprecated)"
 	depends on BLK_DEV_MD
 	help
 	  The "faulty" module allows for a block device that occasionally returns

drivers/md/md-bitmap.c

@@ -2616,7 +2616,7 @@ static struct attribute *md_bitmap_attrs[] = {
 	&max_backlog_used.attr,
 	NULL
 };
-struct attribute_group md_bitmap_group = {
+const struct attribute_group md_bitmap_group = {
 	.name = "bitmap",
 	.attrs = md_bitmap_attrs,
 };

drivers/md/md-faulty.c

@@ -357,7 +357,7 @@ static void raid_exit(void)
 module_init(raid_init);
 module_exit(raid_exit);
 MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("Fault injection personality for MD");
+MODULE_DESCRIPTION("Fault injection personality for MD (deprecated)");
 MODULE_ALIAS("md-personality-10"); /* faulty */
 MODULE_ALIAS("md-faulty");
 MODULE_ALIAS("md-level--5");

drivers/md/md-linear.c

@@ -312,7 +312,7 @@ static void linear_exit (void)
 module_init(linear_init);
 module_exit(linear_exit);
 MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("Linear device concatenation personality for MD");
+MODULE_DESCRIPTION("Linear device concatenation personality for MD (deprecated)");
 MODULE_ALIAS("md-personality-1"); /* LINEAR - deprecated*/
 MODULE_ALIAS("md-linear");
 MODULE_ALIAS("md-level--1");

drivers/md/md-multipath.c

@@ -471,7 +471,7 @@ static void __exit multipath_exit (void)
 module_init(multipath_init);
 module_exit(multipath_exit);
 MODULE_LICENSE("GPL");
-MODULE_DESCRIPTION("simple multi-path personality for MD");
+MODULE_DESCRIPTION("simple multi-path personality for MD (deprecated)");
 MODULE_ALIAS("md-personality-7"); /* MULTIPATH */
 MODULE_ALIAS("md-multipath");
 MODULE_ALIAS("md-level--4");

drivers/md/md.c

@@ -441,30 +441,6 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
 }
 EXPORT_SYMBOL(md_handle_request);
 
-struct md_io {
-	struct mddev *mddev;
-	bio_end_io_t *orig_bi_end_io;
-	void *orig_bi_private;
-	struct block_device *orig_bi_bdev;
-	unsigned long start_time;
-};
-
-static void md_end_io(struct bio *bio)
-{
-	struct md_io *md_io = bio->bi_private;
-	struct mddev *mddev = md_io->mddev;
-
-	bio_end_io_acct_remapped(bio, md_io->start_time, md_io->orig_bi_bdev);
-
-	bio->bi_end_io = md_io->orig_bi_end_io;
-	bio->bi_private = md_io->orig_bi_private;
-
-	mempool_free(md_io, &mddev->md_io_pool);
-
-	if (bio->bi_end_io)
-		bio->bi_end_io(bio);
-}
-
 static blk_qc_t md_submit_bio(struct bio *bio)
 {
 	const int rw = bio_data_dir(bio);
@@ -489,21 +465,6 @@ static blk_qc_t md_submit_bio(struct bio *bio)
 		return BLK_QC_T_NONE;
 	}
 
-	if (bio->bi_end_io != md_end_io) {
-		struct md_io *md_io;
-
-		md_io = mempool_alloc(&mddev->md_io_pool, GFP_NOIO);
-		md_io->mddev = mddev;
-		md_io->orig_bi_end_io = bio->bi_end_io;
-		md_io->orig_bi_private = bio->bi_private;
-		md_io->orig_bi_bdev = bio->bi_bdev;
-
-		bio->bi_end_io = md_end_io;
-		bio->bi_private = md_io;
-
-		md_io->start_time = bio_start_io_acct(bio);
-	}
-
 	/* bio could be mergeable after passing to underlayer */
 	bio->bi_opf &= ~REQ_NOMERGE;
 
@@ -824,7 +785,7 @@ static struct mddev *mddev_alloc(dev_t unit)
 	return ERR_PTR(error);
 }
 
-static struct attribute_group md_redundancy_group;
+static const struct attribute_group md_redundancy_group;
 
 void mddev_unlock(struct mddev *mddev)
 {
@@ -841,7 +802,7 @@ void mddev_unlock(struct mddev *mddev)
 		 * test it under the same mutex to ensure its correct value
 		 * is seen.
 		 */
-		struct attribute_group *to_remove = mddev->to_remove;
+		const struct attribute_group *to_remove = mddev->to_remove;
 		mddev->to_remove = NULL;
 		mddev->sysfs_active = 1;
 		mutex_unlock(&mddev->reconfig_mutex);
@@ -2379,7 +2340,15 @@ int md_integrity_register(struct mddev *mddev)
 			       bdev_get_integrity(reference->bdev));
 
 	pr_debug("md: data integrity enabled on %s\n", mdname(mddev));
-	if (bioset_integrity_create(&mddev->bio_set, BIO_POOL_SIZE)) {
+	if (bioset_integrity_create(&mddev->bio_set, BIO_POOL_SIZE) ||
+	    (mddev->level != 1 && mddev->level != 10 &&
+	     bioset_integrity_create(&mddev->io_acct_set, BIO_POOL_SIZE))) {
+		/*
+		 * No need to handle the failure of bioset_integrity_create,
+		 * because the function is called by md_run() -> pers->run(),
+		 * md_run calls bioset_exit -> bioset_integrity_free in case
+		 * of failure case.
+		 */
 		pr_err("md: failed to create integrity pool for %s\n",
 		       mdname(mddev));
 		return -EINVAL;
@@ -5538,7 +5507,7 @@ static struct attribute *md_redundancy_attrs[] = {
 	&md_degraded.attr,
 	NULL,
 };
-static struct attribute_group md_redundancy_group = {
+static const struct attribute_group md_redundancy_group = {
 	.name = NULL,
 	.attrs = md_redundancy_attrs,
 };
@@ -5608,7 +5577,8 @@ static void md_free(struct kobject *ko)
 
 	bioset_exit(&mddev->bio_set);
 	bioset_exit(&mddev->sync_set);
-	mempool_exit(&mddev->md_io_pool);
+	if (mddev->level != 1 && mddev->level != 10)
+		bioset_exit(&mddev->io_acct_set);
 	kfree(mddev);
 }
 
@@ -5705,11 +5675,6 @@ static int md_alloc(dev_t dev, char *name)
 		 */
 		mddev->hold_active = UNTIL_STOP;
 
-	error = mempool_init_kmalloc_pool(&mddev->md_io_pool, BIO_POOL_SIZE,
-					  sizeof(struct md_io));
-	if (error)
-		goto abort;
-
 	error = -ENOMEM;
 	mddev->queue = blk_alloc_queue(NUMA_NO_NODE);
 	if (!mddev->queue)
@@ -5907,7 +5872,14 @@ int md_run(struct mddev *mddev)
 	if (!bioset_initialized(&mddev->sync_set)) {
 		err = bioset_init(&mddev->sync_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
 		if (err)
-			return err;
+			goto exit_bio_set;
+	}
+	if (mddev->level != 1 && mddev->level != 10 &&
+	    !bioset_initialized(&mddev->io_acct_set)) {
+		err = bioset_init(&mddev->io_acct_set, BIO_POOL_SIZE,
+				  offsetof(struct md_io_acct, bio_clone), 0);
+		if (err)
+			goto exit_sync_set;
 	}
 
 	spin_lock(&pers_lock);
@@ -6035,6 +6007,7 @@ int md_run(struct mddev *mddev)
 			blk_queue_flag_set(QUEUE_FLAG_NONROT, mddev->queue);
 		else
 			blk_queue_flag_clear(QUEUE_FLAG_NONROT, mddev->queue);
+		blk_queue_flag_set(QUEUE_FLAG_IO_STAT, mddev->queue);
 	}
 	if (pers->sync_request) {
 		if (mddev->kobj.sd &&
@@ -6084,8 +6057,12 @@ int md_run(struct mddev *mddev)
 	module_put(pers->owner);
 	md_bitmap_destroy(mddev);
 abort:
-	bioset_exit(&mddev->bio_set);
+	if (mddev->level != 1 && mddev->level != 10)
+		bioset_exit(&mddev->io_acct_set);
+exit_sync_set:
 	bioset_exit(&mddev->sync_set);
+exit_bio_set:
+	bioset_exit(&mddev->bio_set);
 	return err;
 }
 EXPORT_SYMBOL_GPL(md_run);
@@ -6309,6 +6286,8 @@ void md_stop(struct mddev *mddev)
 	__md_stop(mddev);
 	bioset_exit(&mddev->bio_set);
 	bioset_exit(&mddev->sync_set);
+	if (mddev->level != 1 && mddev->level != 10)
+		bioset_exit(&mddev->io_acct_set);
 }
 
 EXPORT_SYMBOL_GPL(md_stop);
@@ -8613,6 +8592,41 @@ void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
 }
 EXPORT_SYMBOL_GPL(md_submit_discard_bio);
 
+static void md_end_io_acct(struct bio *bio)
+{
+	struct md_io_acct *md_io_acct = bio->bi_private;
+	struct bio *orig_bio = md_io_acct->orig_bio;
+
+	orig_bio->bi_status = bio->bi_status;
+
+	bio_end_io_acct(orig_bio, md_io_acct->start_time);
+	bio_put(bio);
+	bio_endio(orig_bio);
+}
+
+/*
+ * Used by personalities that don't already clone the bio and thus can't
+ * easily add the timestamp to their extended bio structure.
+ */
+void md_account_bio(struct mddev *mddev, struct bio **bio)
+{
+	struct md_io_acct *md_io_acct;
+	struct bio *clone;
+
+	if (!blk_queue_io_stat((*bio)->bi_bdev->bd_disk->queue))
+		return;
+
+	clone = bio_clone_fast(*bio, GFP_NOIO, &mddev->io_acct_set);
+	md_io_acct = container_of(clone, struct md_io_acct, bio_clone);
+	md_io_acct->orig_bio = *bio;
+	md_io_acct->start_time = bio_start_io_acct(*bio);
+
+	clone->bi_end_io = md_end_io_acct;
+	clone->bi_private = md_io_acct;
+	*bio = clone;
+}
+EXPORT_SYMBOL_GPL(md_account_bio);
+
 /* md_allow_write(mddev)
  * Calling this ensures that the array is marked 'active' so that writes
  * may proceed without blocking.  It is important to call this before

drivers/md/md.h

@@ -481,13 +481,13 @@ struct mddev {
 	atomic_t			max_corr_read_errors; /* max read retries */
 	struct list_head		all_mddevs;
 
-	struct attribute_group		*to_remove;
+	const struct attribute_group	*to_remove;
 
 	struct bio_set			bio_set;
 	struct bio_set			sync_set; /* for sync operations like
 						   * metadata and bitmap writes
 						   */
-	mempool_t			md_io_pool;
+	struct bio_set			io_acct_set; /* for raid0 and raid5 io accounting */
 
 	/* Generic flush handling.
 	 * The last to finish preflush schedules a worker to submit
@@ -613,7 +613,7 @@ struct md_sysfs_entry {
 	ssize_t (*show)(struct mddev *, char *);
 	ssize_t (*store)(struct mddev *, const char *, size_t);
 };
-extern struct attribute_group md_bitmap_group;
+extern const struct attribute_group md_bitmap_group;
 
 static inline struct kernfs_node *sysfs_get_dirent_safe(struct kernfs_node *sd, char *name)
 {
@@ -684,6 +684,12 @@ struct md_thread {
 	void			*private;
 };
 
+struct md_io_acct {
+	struct bio *orig_bio;
+	unsigned long start_time;
+	struct bio bio_clone;
+};
+
 #define THREAD_WAKEUP  0
 
 static inline void safe_put_page(struct page *p)
@@ -715,6 +721,7 @@ extern void md_error(struct mddev *mddev, struct md_rdev *rdev);
 extern void md_finish_reshape(struct mddev *mddev);
 void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
 			struct bio *bio, sector_t start, sector_t size);
+void md_account_bio(struct mddev *mddev, struct bio **bio);
 
 extern bool __must_check md_flush_request(struct mddev *mddev, struct bio *bio);
 extern void md_super_write(struct mddev *mddev, struct md_rdev *rdev,

drivers/md/raid0.c

@@ -546,6 +546,9 @@ static bool raid0_make_request(struct mddev *mddev, struct bio *bio)
 		bio = split;
 	}
 
+	if (bio->bi_pool != &mddev->bio_set)
+		md_account_bio(mddev, &bio);
+
 	orig_sector = sector;
 	zone = find_zone(mddev->private, &sector);
 	switch (conf->layout) {

drivers/md/raid1.c

@@ -300,6 +300,8 @@ static void call_bio_endio(struct r1bio *r1_bio)
 	if (!test_bit(R1BIO_Uptodate, &r1_bio->state))
 		bio->bi_status = BLK_STS_IOERR;
 
+	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
+		bio_end_io_acct(bio, r1_bio->start_time);
 	bio_endio(bio);
 }
 
@@ -1210,7 +1212,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 	const unsigned long do_sync = (bio->bi_opf & REQ_SYNC);
 	int max_sectors;
 	int rdisk;
-	bool print_msg = !!r1_bio;
+	bool r1bio_existed = !!r1_bio;
 	char b[BDEVNAME_SIZE];
 
 	/*
@@ -1220,7 +1222,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 	 */
 	gfp_t gfp = r1_bio ? (GFP_NOIO | __GFP_HIGH) : GFP_NOIO;
 
-	if (print_msg) {
+	if (r1bio_existed) {
 		/* Need to get the block device name carefully */
 		struct md_rdev *rdev;
 		rcu_read_lock();
@@ -1252,7 +1254,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 
 	if (rdisk < 0) {
 		/* couldn't find anywhere to read from */
-		if (print_msg) {
+		if (r1bio_existed) {
 			pr_crit_ratelimited("md/raid1:%s: %s: unrecoverable I/O read error for block %llu\n",
 					    mdname(mddev),
 					    b,
@@ -1263,7 +1265,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 	}
 	mirror = conf->mirrors + rdisk;
 
-	if (print_msg)
+	if (r1bio_existed)
 		pr_info_ratelimited("md/raid1:%s: redirecting sector %llu to other mirror: %s\n",
 				    mdname(mddev),
 				    (unsigned long long)r1_bio->sector,
@@ -1292,6 +1294,9 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio,
 
 	r1_bio->read_disk = rdisk;
 
+	if (!r1bio_existed && blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
+		r1_bio->start_time = bio_start_io_acct(bio);
+
 	read_bio = bio_clone_fast(bio, gfp, &mddev->bio_set);
 
 	r1_bio->bios[rdisk] = read_bio;
@@ -1461,6 +1466,8 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 		r1_bio->sectors = max_sectors;
 	}
 
+	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
+		r1_bio->start_time = bio_start_io_acct(bio);
 	atomic_set(&r1_bio->remaining, 1);
 	atomic_set(&r1_bio->behind_remaining, 0);
 

drivers/md/raid1.h

@@ -158,6 +158,7 @@ struct r1bio {
 	sector_t		sector;
 	int			sectors;
 	unsigned long		state;
+	unsigned long		start_time;
 	struct mddev		*mddev;
 	/*
 	 * original bio going to /dev/mdx

drivers/md/raid10.c

@@ -297,6 +297,8 @@ static void raid_end_bio_io(struct r10bio *r10_bio)
 	if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
 		bio->bi_status = BLK_STS_IOERR;
 
+	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
+		bio_end_io_acct(bio, r10_bio->start_time);
 	bio_endio(bio);
 	/*
 	 * Wake up any possible resync thread that waits for the device
@@ -1184,6 +1186,8 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
 	}
 	slot = r10_bio->read_slot;
 
+	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
+		r10_bio->start_time = bio_start_io_acct(bio);
 	read_bio = bio_clone_fast(bio, gfp, &mddev->bio_set);
 
 	r10_bio->devs[slot].bio = read_bio;
@@ -1483,6 +1487,8 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
 		r10_bio->master_bio = bio;
 	}
 
+	if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
+		r10_bio->start_time = bio_start_io_acct(bio);
 	atomic_set(&r10_bio->remaining, 1);
 	md_bitmap_startwrite(mddev->bitmap, r10_bio->sector, r10_bio->sectors, 0);
 

drivers/md/raid10.h

@@ -124,6 +124,7 @@ struct r10bio {
 	sector_t		sector;	/* virtual sector number */
 	int			sectors;
 	unsigned long		state;
+	unsigned long		start_time;
 	struct mddev		*mddev;
 	/*
 	 * original bio going to /dev/mdx

drivers/md/raid5.c

@@ -5364,11 +5364,13 @@ static struct bio *remove_bio_from_retry(struct r5conf *conf,
  */
 static void raid5_align_endio(struct bio *bi)
 {
-	struct bio* raid_bi  = bi->bi_private;
+	struct md_io_acct *md_io_acct = bi->bi_private;
+	struct bio *raid_bi = md_io_acct->orig_bio;
 	struct mddev *mddev;
 	struct r5conf *conf;
 	struct md_rdev *rdev;
 	blk_status_t error = bi->bi_status;
+	unsigned long start_time = md_io_acct->start_time;
 
 	bio_put(bi);
 
@@ -5380,6 +5382,8 @@ static void raid5_align_endio(struct bio *bi)
 	rdev_dec_pending(rdev, conf->mddev);
 
 	if (!error) {
+		if (blk_queue_io_stat(raid_bi->bi_bdev->bd_disk->queue))
+			bio_end_io_acct(raid_bi, start_time);
 		bio_endio(raid_bi);
 		if (atomic_dec_and_test(&conf->active_aligned_reads))
 			wake_up(&conf->wait_for_quiescent);
@@ -5398,6 +5402,8 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
 	struct md_rdev *rdev;
 	sector_t sector, end_sector, first_bad;
 	int bad_sectors, dd_idx;
+	struct md_io_acct *md_io_acct;
+	bool did_inc;
 
 	if (!in_chunk_boundary(mddev, raid_bio)) {
 		pr_debug("%s: non aligned\n", __func__);
@@ -5427,29 +5433,46 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
 	atomic_inc(&rdev->nr_pending);
 	rcu_read_unlock();
 
-	align_bio = bio_clone_fast(raid_bio, GFP_NOIO, &mddev->bio_set);
-	bio_set_dev(align_bio, rdev->bdev);
-	align_bio->bi_end_io = raid5_align_endio;
-	align_bio->bi_private = raid_bio;
-	align_bio->bi_iter.bi_sector = sector;
-
-	raid_bio->bi_next = (void *)rdev;
-
-	if (is_badblock(rdev, sector, bio_sectors(align_bio), &first_bad,
+	if (is_badblock(rdev, sector, bio_sectors(raid_bio), &first_bad,
 			&bad_sectors)) {
-		bio_put(align_bio);
+		bio_put(raid_bio);
 		rdev_dec_pending(rdev, mddev);
 		return 0;
 	}
 
+	align_bio = bio_clone_fast(raid_bio, GFP_NOIO, &mddev->io_acct_set);
+	md_io_acct = container_of(align_bio, struct md_io_acct, bio_clone);
+	raid_bio->bi_next = (void *)rdev;
+	if (blk_queue_io_stat(raid_bio->bi_bdev->bd_disk->queue))
+		md_io_acct->start_time = bio_start_io_acct(raid_bio);
+	md_io_acct->orig_bio = raid_bio;
+
+	bio_set_dev(align_bio, rdev->bdev);
+	align_bio->bi_end_io = raid5_align_endio;
+	align_bio->bi_private = md_io_acct;
+	align_bio->bi_iter.bi_sector = sector;
+
 	/* No reshape active, so we can trust rdev->data_offset */
 	align_bio->bi_iter.bi_sector += rdev->data_offset;
 
+	did_inc = false;
+	if (conf->quiesce == 0) {
+		atomic_inc(&conf->active_aligned_reads);
+		did_inc = true;
+	}
+	/* need a memory barrier to detect the race with raid5_quiesce() */
+	if (!did_inc || smp_load_acquire(&conf->quiesce) != 0) {
+		/* quiesce is in progress, so we need to undo io activation and wait
+		 * for it to finish
+		 */
+		if (did_inc && atomic_dec_and_test(&conf->active_aligned_reads))
+			wake_up(&conf->wait_for_quiescent);
 		spin_lock_irq(&conf->device_lock);
 		wait_event_lock_irq(conf->wait_for_quiescent, conf->quiesce == 0,
 				    conf->device_lock);
 		atomic_inc(&conf->active_aligned_reads);
 		spin_unlock_irq(&conf->device_lock);
+	}
 
 	if (mddev->gendisk)
 		trace_block_bio_remap(align_bio, disk_devt(mddev->gendisk),
@@ -5798,6 +5821,7 @@ static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 	last_sector = bio_end_sector(bi);
 	bi->bi_next = NULL;
 
+	md_account_bio(mddev, &bi);
 	prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
 	for (; logical_sector < last_sector; logical_sector += RAID5_STRIPE_SECTORS(conf)) {
 		int previous;
@@ -6930,7 +6954,7 @@ static struct attribute *raid5_attrs[] =  {
 	&ppl_write_hint.attr,
 	NULL,
 };
-static struct attribute_group raid5_attrs_group = {
+static const struct attribute_group raid5_attrs_group = {
 	.name = NULL,
 	.attrs = raid5_attrs,
 };
@@ -8336,7 +8360,10 @@ static void raid5_quiesce(struct mddev *mddev, int quiesce)
 		 * active stripes can drain
 		 */
 		r5c_flush_cache(conf, INT_MAX);
-		conf->quiesce = 2;
+		/* need a memory barrier to make sure read_one_chunk() sees
+		 * quiesce started and reverts to slow (locked) path.
+		 */
+		smp_store_release(&conf->quiesce, 2);
 		wait_event_cmd(conf->wait_for_quiescent,
 				    atomic_read(&conf->active_stripes) == 0 &&
 				    atomic_read(&conf->active_aligned_reads) == 0,