[PATCH v2] md/raid5: use dedicated llist for stripe plug

["Li Youhong" <dayou5941@163.com>]

From: Li Youhong <liyouhong@kylinos.cn>

release_stripe_plug() and do_release_stripe() share sh->lru.
release_stripe_plug() sets STRIPE_ON_UNPLUG_LIST and
list_add_tail()s sh->lru onto raid5_plug_cb.list without
device_lock. do_release_stripe() holds device_lock and, when the
last reference drops, list_add()s the same lru onto a handle or
inactive list.

Two list_add()s on one node corrupt it. sh->lru can be
reinitialized into a self-loop while raid5_plug_cb.list still
points at that stripe. raid5_unplug() then walks the list under
device_lock with IRQs disabled and never finishes. Other CPUs
waiting for the same lock hard-lockup.

Add a dedicated llist_node, unplug_list, to stripe_head, as
release_list is used for released_stripes.

Fixes: 8811b5968f62 ("raid5: make_request use batch stripe release")
Suggested-by: Yu Kuai <yukuai@fygo.io>
Cc: stable@vger.kernel.org
Signed-off-by: Li Youhong <liyouhong@kylinos.cn>
---
v2:
- Drop taking device_lock in release_stripe_plug(). Add a dedicated
  unplug_list.
- v1: link: https://lore.kernel.org/linux-raid/20260902095307.358569-1-dayou5941@163.com/

---
 drivers/md/raid5.c | 52 ++++++++++++++++++++++++++--------------------------
 drivers/md/raid5.h |  1 +
 2 files changed, 27 insertions(+), 26 deletions(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index b91545ce090d..9dabbf9743d7 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5710,7 +5710,7 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
 
 struct raid5_plug_cb {
 	struct blk_plug_cb	cb;
-	struct list_head	list;
+	struct llist_head	unplug_list;
 	struct list_head	temp_inactive_list[NR_STRIPE_HASH_LOCKS];
 };
 
@@ -5718,34 +5718,33 @@ static void raid5_unplug(struct blk_plug_cb *blk_cb, bool from_schedule)
 {
 	struct raid5_plug_cb *cb = container_of(
 		blk_cb, struct raid5_plug_cb, cb);
-	struct stripe_head *sh;
+	struct stripe_head *sh, *tmp;
 	struct mddev *mddev = cb->cb.data;
 	struct r5conf *conf = mddev->private;
+	struct llist_node *head;
 	int cnt = 0;
 	int hash;
 
-	if (cb->list.next && !list_empty(&cb->list)) {
-		spin_lock_irq(&conf->device_lock);
-		while (!list_empty(&cb->list)) {
-			sh = list_first_entry(&cb->list, struct stripe_head, lru);
-			list_del_init(&sh->lru);
-			/*
-			 * avoid race release_stripe_plug() sees
-			 * STRIPE_ON_UNPLUG_LIST clear but the stripe
-			 * is still in our list
-			 */
-			smp_mb__before_atomic();
-			clear_bit(STRIPE_ON_UNPLUG_LIST, &sh->state);
-			/*
-			 * STRIPE_ON_RELEASE_LIST could be set here. In that
-			 * case, the count is always > 1 here
-			 */
-			hash = sh->hash_lock_index;
-			__release_stripe(conf, sh, &cb->temp_inactive_list[hash]);
-			cnt++;
-		}
-		spin_unlock_irq(&conf->device_lock);
+	head = llist_del_all(&cb->unplug_list);
+	head = llist_reverse_order(head);
+	spin_lock_irq(&conf->device_lock);
+	llist_for_each_entry_safe(sh, tmp, head, unplug_list) {
+		/*
+		 * avoid race release_stripe_plug() sees
+		 * STRIPE_ON_UNPLUG_LIST clear but the stripe
+		 * is still in our list
+		 */
+		smp_mb__before_atomic();
+		clear_bit(STRIPE_ON_UNPLUG_LIST, &sh->state);
+		/*
+		 * STRIPE_ON_RELEASE_LIST could be set here. In that
+		 * case, the count is always > 1 here
+		 */
+		hash = sh->hash_lock_index;
+		__release_stripe(conf, sh, &cb->temp_inactive_list[hash]);
+		cnt++;
 	}
+	spin_unlock_irq(&conf->device_lock);
 	release_inactive_stripe_list(conf, cb->temp_inactive_list,
 				     NR_STRIPE_HASH_LOCKS);
 	if (!mddev_is_dm(mddev))
@@ -5768,15 +5767,16 @@ static void release_stripe_plug(struct mddev *mddev,
 
 	cb = container_of(blk_cb, struct raid5_plug_cb, cb);
 
-	if (cb->list.next == NULL) {
+	if (!cb->temp_inactive_list[0].next) {
 		int i;
-		INIT_LIST_HEAD(&cb->list);
+
+		init_llist_head(&cb->unplug_list);
 		for (i = 0; i < NR_STRIPE_HASH_LOCKS; i++)
 			INIT_LIST_HEAD(cb->temp_inactive_list + i);
 	}
 
 	if (!test_and_set_bit(STRIPE_ON_UNPLUG_LIST, &sh->state))
-		list_add_tail(&sh->lru, &cb->list);
+		llist_add(&sh->unplug_list, &cb->unplug_list);
 	else
 		raid5_release_stripe(sh);
 }
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index cb5feae04db2..e314f17eb949 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -201,6 +201,7 @@ struct stripe_head {
 	struct hlist_node	hash;
 	struct list_head	lru;	      /* inactive_list or handle_list */
 	struct llist_node	release_list;
+	struct llist_node	unplug_list;
 	struct r5conf		*raid_conf;
 	short			generation;	/* increments with every
 						 * reshape */
-- 
2.25.1