md: fix deadlock between mddev_suspend() and md_write_start()

If mddev_suspend() races with md_write_start() we can deadlock
with mddev_suspend() waiting for the request that is currently
in md_write_start() to complete the ->make_request() call,
and md_write_start() waiting for the metadata to be updated
to mark the array as 'dirty'.
As metadata updates done by md_check_recovery() only happen then
the mddev_lock() can be claimed, and as mddev_suspend() is often
called with the lock held, these threads wait indefinitely for each
other.

We fix this by having md_write_start() abort if mddev_suspend()
is happening, and ->make_request() aborts if md_write_start()
aborted.
md_make_request() can detect this abort, decrease the ->active_io
count, and wait for mddev_suspend().

Reported-by: Nix <[e-mail]>
Fix: 68866e425be2(MD: no sync IO while suspended)
Cc: [e-mail]
Signed-off-by: NeilBrown <[e-mail]>
Signed-off-by: Shaohua Li <[e-mail]>

drivers/md/faulty.c

···
 		conf->nfaults = n+1;
 }
 
-static void faulty_make_request(struct mddev *mddev, struct bio *bio)
+static bool faulty_make_request(struct mddev *mddev, struct bio *bio)
 {
 	struct faulty_conf *conf = mddev->private;
 	int failit = 0;
···
 			 * just fail immediately
 			 */
 			bio_io_error(bio);
-			return;
+			return true;
 		}
 
 		if (check_sector(conf, bio->bi_iter.bi_sector,
···
 		bio->bi_bdev = conf->rdev->bdev;
 
 	generic_make_request(bio);
+	return true;
 }
 
 static void faulty_status(struct seq_file *seq, struct mddev *mddev)

drivers/md/linear.c

···
 	kfree(conf);
 }
 
-static void linear_make_request(struct mddev *mddev, struct bio *bio)
+static bool linear_make_request(struct mddev *mddev, struct bio *bio)
 {
 	char b[BDEVNAME_SIZE];
 	struct dev_info *tmp_dev;
···
 
 	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
 		md_flush_request(mddev, bio);
-		return;
+		return true;
 	}
 
 	tmp_dev = which_dev(mddev, bio_sector);
···
 		mddev_check_write_zeroes(mddev, bio);
 		generic_make_request(bio);
 	}
-	return;
+	return true;
 
 out_of_bounds:
 	pr_err("md/linear:%s: make_request: Sector %llu out of bounds on dev %s: %llu sectors, offset %llu\n",
···
 	       (unsigned long long)tmp_dev->rdev->sectors,
 	       (unsigned long long)start_sector);
 	bio_io_error(bio);
+	return true;
 }
 
 static void linear_status (struct seq_file *seq, struct mddev *mddev)

drivers/md/md.c

···
 		bio_endio(bio);
 		return BLK_QC_T_NONE;
 	}
-	smp_rmb(); /* Ensure implications of  'active' are visible */
+check_suspended:
 	rcu_read_lock();
 	if (mddev->suspended) {
 		DEFINE_WAIT(__wait);
···
 	sectors = bio_sectors(bio);
 	/* bio could be mergeable after passing to underlayer */
 	bio->bi_opf &= ~REQ_NOMERGE;
-	mddev->pers->make_request(mddev, bio);
+	if (!mddev->pers->make_request(mddev, bio)) {
+		atomic_dec(&mddev->active_io);
+		wake_up(&mddev->sb_wait);
+		goto check_suspended;
+	}
 
 	cpu = part_stat_lock();
 	part_stat_inc(cpu, &mddev->gendisk->part0, ios[rw]);
···
 	if (mddev->suspended++)
 		return;
 	synchronize_rcu();
+	wake_up(&mddev->sb_wait);
 	wait_event(mddev->sb_wait, atomic_read(&mddev->active_io) == 0);
 	mddev->pers->quiesce(mddev, 1);
 
···
  * If we need to update some array metadata (e.g. 'active' flag
  * in superblock) before writing, schedule a superblock update
  * and wait for it to complete.
+ * A return value of 'false' means that the write wasn't recorded
+ * and cannot proceed as the array is being suspend.
  */
-void md_write_start(struct mddev *mddev, struct bio *bi)
+bool md_write_start(struct mddev *mddev, struct bio *bi)
 {
 	int did_change = 0;
 	if (bio_data_dir(bi) != WRITE)
-		return;
+		return true;
 
 	BUG_ON(mddev->ro == 1);
 	if (mddev->ro == 2) {
···
 	if (did_change)
 		sysfs_notify_dirent_safe(mddev->sysfs_state);
 	wait_event(mddev->sb_wait,
-		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));
+		   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) && !mddev->suspended);
+	if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
+		percpu_ref_put(&mddev->writes_pending);
+		return false;
+	}
+	return true;
 }
 EXPORT_SYMBOL(md_write_start);
 

drivers/md/md.h

···
 	int level;
 	struct list_head list;
 	struct module *owner;
-	void (*make_request)(struct mddev *mddev, struct bio *bio);
+	bool (*make_request)(struct mddev *mddev, struct bio *bio);
 	int (*run)(struct mddev *mddev);
 	void (*free)(struct mddev *mddev, void *priv);
 	void (*status)(struct seq_file *seq, struct mddev *mddev);
···
 extern void md_check_recovery(struct mddev *mddev);
 extern void md_reap_sync_thread(struct mddev *mddev);
 extern int mddev_init_writes_pending(struct mddev *mddev);
-extern void md_write_start(struct mddev *mddev, struct bio *bi);
+extern bool md_write_start(struct mddev *mddev, struct bio *bi);
 extern void md_write_inc(struct mddev *mddev, struct bio *bi);
 extern void md_write_end(struct mddev *mddev);
 extern void md_done_sync(struct mddev *mddev, int blocks, int ok);

drivers/md/multipath.c

···
 	rdev_dec_pending(rdev, conf->mddev);
 }
 
-static void multipath_make_request(struct mddev *mddev, struct bio * bio)
+static bool multipath_make_request(struct mddev *mddev, struct bio * bio)
 {
 	struct mpconf *conf = mddev->private;
 	struct multipath_bh * mp_bh;
···
 
 	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
 		md_flush_request(mddev, bio);
-		return;
+		return true;
 	}
 
 	mp_bh = mempool_alloc(conf->pool, GFP_NOIO);
···
 	if (mp_bh->path < 0) {
 		bio_io_error(bio);
 		mempool_free(mp_bh, conf->pool);
-		return;
+		return true;
 	}
 	multipath = conf->multipaths + mp_bh->path;
 
···
 	mddev_check_writesame(mddev, &mp_bh->bio);
 	mddev_check_write_zeroes(mddev, &mp_bh->bio);
 	generic_make_request(&mp_bh->bio);
-	return;
+	return true;
 }
 
 static void multipath_status(struct seq_file *seq, struct mddev *mddev)

drivers/md/raid0.c

···
 	bio_endio(bio);
 }
 
-static void raid0_make_request(struct mddev *mddev, struct bio *bio)
+static bool raid0_make_request(struct mddev *mddev, struct bio *bio)
 {
 	struct strip_zone *zone;
 	struct md_rdev *tmp_dev;
···
 
 	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
 		md_flush_request(mddev, bio);
-		return;
+		return true;
 	}
 
 	if (unlikely((bio_op(bio) == REQ_OP_DISCARD))) {
 		raid0_handle_discard(mddev, bio);
-		return;
+		return true;
 	}
 
 	bio_sector = bio->bi_iter.bi_sector;
···
 	mddev_check_writesame(mddev, bio);
 	mddev_check_write_zeroes(mddev, bio);
 	generic_make_request(bio);
+	return true;
 }
 
 static void raid0_status(struct seq_file *seq, struct mddev *mddev)

drivers/md/raid1.c

···
 	 * Continue immediately if no resync is active currently.
 	 */
 
-	md_write_start(mddev, bio); /* wait on superblock update early */
 
 	if ((bio_end_sector(bio) > mddev->suspend_lo &&
 	    bio->bi_iter.bi_sector < mddev->suspend_hi) ||
···
 	wake_up(&conf->wait_barrier);
 }
 
-static void raid1_make_request(struct mddev *mddev, struct bio *bio)
+static bool raid1_make_request(struct mddev *mddev, struct bio *bio)
 {
 	sector_t sectors;
 
 	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
 		md_flush_request(mddev, bio);
-		return;
+		return true;
 	}
 
 	/*
···
 
 	if (bio_data_dir(bio) == READ)
 		raid1_read_request(mddev, bio, sectors, NULL);
-	else
+	else {
+		if (!md_write_start(mddev,bio))
+			return false;
 		raid1_write_request(mddev, bio, sectors);
+	}
+	return true;
 }
 
 static void raid1_status(struct seq_file *seq, struct mddev *mddev)

drivers/md/raid10.c

···
 	sector_t sectors;
 	int max_sectors;
 
-	md_write_start(mddev, bio);
-
 	/*
 	 * Register the new request and wait if the reconstruction
 	 * thread has put up a bar for new requests.
···
 		raid10_write_request(mddev, bio, r10_bio);
 }
 
-static void raid10_make_request(struct mddev *mddev, struct bio *bio)
+static bool raid10_make_request(struct mddev *mddev, struct bio *bio)
 {
 	struct r10conf *conf = mddev->private;
 	sector_t chunk_mask = (conf->geo.chunk_mask & conf->prev.chunk_mask);
···
 
 	if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
 		md_flush_request(mddev, bio);
-		return;
+		return true;
 	}
+
+	if (!md_write_start(mddev, bio))
+		return false;
 
 	/*
 	 * If this request crosses a chunk boundary, we need to split
···
 
 	/* In case raid10d snuck in to freeze_array */
 	wake_up(&conf->wait_barrier);
+	return true;
 }
 
 static void raid10_status(struct seq_file *seq, struct mddev *mddev)

drivers/md/raid5.c

···
 	last_sector = bi->bi_iter.bi_sector + (bi->bi_iter.bi_size>>9);
 
 	bi->bi_next = NULL;
-	md_write_start(mddev, bi);
 
 	stripe_sectors = conf->chunk_sectors *
 		(conf->raid_disks - conf->max_degraded);
···
 		release_stripe_plug(mddev, sh);
 	}
 
-	md_write_end(mddev);
 	bio_endio(bi);
 }
 
-static void raid5_make_request(struct mddev *mddev, struct bio * bi)
+static bool raid5_make_request(struct mddev *mddev, struct bio * bi)
 {
 	struct r5conf *conf = mddev->private;
 	int dd_idx;
···
 		int ret = r5l_handle_flush_request(conf->log, bi);
 
 		if (ret == 0)
-			return;
+			return true;
 		if (ret == -ENODEV) {
 			md_flush_request(mddev, bi);
-			return;
+			return true;
 		}
 		/* ret == -EAGAIN, fallback */
 		/*
···
 		do_flush = bi->bi_opf & REQ_PREFLUSH;
 	}
 
+	if (!md_write_start(mddev, bi))
+		return false;
 	/*
 	 * If array is degraded, better not do chunk aligned read because
 	 * later we might have to read it again in order to reconstruct
···
 	    mddev->reshape_position == MaxSector) {
 		bi = chunk_aligned_read(mddev, bi);
 		if (!bi)
-			return;
+			return true;
 	}
 
 	if (unlikely(bio_op(bi) == REQ_OP_DISCARD)) {
 		make_discard_request(mddev, bi);
-		return;
+		md_write_end(mddev);
+		return true;
 	}
 
 	logical_sector = bi->bi_iter.bi_sector & ~((sector_t)STRIPE_SECTORS-1);
 	last_sector = bio_end_sector(bi);
 	bi->bi_next = NULL;
-	md_write_start(mddev, bi);
 
 	prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
 	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
···
 	if (rw == WRITE)
 		md_write_end(mddev);
 	bio_endio(bi);
+	return true;
 }
 
 static sector_t raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks);