md/raid1-10: limit the number of plugged bio

bio can be added to plug infinitely, and following writeback test can
trigger huge amount of plugged bio:

Test script:
modprobe brd rd_nr=4 rd_size=10485760
mdadm -CR /dev/md0 -l10 -n4 /dev/ram[0123] --assume-clean --bitmap=internal
echo 0 > /proc/sys/vm/dirty_background_ratio
fio -filename=/dev/md0 -ioengine=libaio -rw=write -bs=4k -numjobs=1 -iodepth=128 -name=test

Test result:
Monitor /sys/block/md0/inflight will found that inflight keep increasing
until fio finish writing, after running for about 2 minutes:

[root@fedora ~]# cat /sys/block/md0/inflight
       0  4474191

Fix the problem by limiting the number of plugged bio based on the number
of copies for original bio.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230529131106.2123367-8-yukuai1@huaweicloud.com

drivers/md/raid1-10.c

@@ -21,6 +21,7 @@
 #define IO_MADE_GOOD ((struct bio *)2)
 
 #define BIO_SPECIAL(bio) ((unsigned long)bio <= 2)
+#define MAX_PLUG_BIO 32
 
 /* for managing resync I/O pages */
 struct resync_pages {
@@ -31,6 +32,7 @@ struct resync_pages {
 struct raid1_plug_cb {
 	struct blk_plug_cb	cb;
 	struct bio_list		pending;
+	unsigned int		count;
 };
 
 static void rbio_pool_free(void *rbio, void *data)
@@ -129,7 +131,7 @@ static inline void raid1_submit_write(struct bio *bio)
 }
 
 static inline bool raid1_add_bio_to_plug(struct mddev *mddev, struct bio *bio,
-				      blk_plug_cb_fn unplug)
+				      blk_plug_cb_fn unplug, int copies)
 {
 	struct raid1_plug_cb *plug = NULL;
 	struct blk_plug_cb *cb;
@@ -149,6 +151,11 @@ static inline bool raid1_add_bio_to_plug(struct mddev *mddev, struct bio *bio,
 
 	plug = container_of(cb, struct raid1_plug_cb, cb);
 	bio_list_add(&plug->pending, bio);
+	if (++plug->count / MAX_PLUG_BIO >= copies) {
+		list_del(&cb->list);
+		cb->callback(cb, false);
+	}
+
 
 	return true;
 }

drivers/md/raid1.c

@@ -1565,7 +1565,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 					      r1_bio->sector);
 		/* flush_pending_writes() needs access to the rdev so...*/
 		mbio->bi_bdev = (void *)rdev;
-		if (!raid1_add_bio_to_plug(mddev, mbio, raid1_unplug)) {
+		if (!raid1_add_bio_to_plug(mddev, mbio, raid1_unplug, disks)) {
 			spin_lock_irqsave(&conf->device_lock, flags);
 			bio_list_add(&conf->pending_bio_list, mbio);
 			spin_unlock_irqrestore(&conf->device_lock, flags);

drivers/md/raid10.c

@@ -1314,7 +1314,7 @@ static void raid10_write_one_disk(struct mddev *mddev, struct r10bio *r10_bio,
 
 	atomic_inc(&r10_bio->remaining);
 
-	if (!raid1_add_bio_to_plug(mddev, mbio, raid10_unplug)) {
+	if (!raid1_add_bio_to_plug(mddev, mbio, raid10_unplug, conf->copies)) {
 		spin_lock_irqsave(&conf->device_lock, flags);
 		bio_list_add(&conf->pending_bio_list, mbio);
 		spin_unlock_irqrestore(&conf->device_lock, flags);