[PATCH v4 1/4] blk-cgroup: protect q->blkg_list iteration in blkg_destroy_all() with blkcg_mutex

[Yu Kuai <yukuai@kernel.org>]

From: Yu Kuai <yukuai@fygo.io>

blkg_destroy_all() iterates q->blkg_list without holding blkcg_mutex,
which can race with blkg_free_workfn() that removes blkgs from the list
while holding blkcg_mutex.

Add blkcg_mutex protection around the q->blkg_list iteration to prevent
potential list corruption or use-after-free issues.

Reviewed-by: Tang Yizhou <yizhou.tang@shopee.com>
Signed-off-by: Yu Kuai <yukuai@fygo.io>
---
 block/blk-cgroup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index d9676126c5b5..eb0cfb10b859 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -569,6 +569,7 @@ static void blkg_destroy_all(struct gendisk *disk)
 	int i;
 
 restart:
+	mutex_lock(&q->blkcg_mutex);
 	spin_lock_irq(&q->queue_lock);
 	list_for_each_entry(blkg, &q->blkg_list, q_node) {
 		struct blkcg *blkcg = blkg->blkcg;
@@ -587,6 +588,7 @@ static void blkg_destroy_all(struct gendisk *disk)
 		if (!(--count)) {
 			count = BLKG_DESTROY_BATCH_SIZE;
 			spin_unlock_irq(&q->queue_lock);
+			mutex_unlock(&q->blkcg_mutex);
 			cond_resched();
 			goto restart;
 		}
@@ -606,6 +608,7 @@ static void blkg_destroy_all(struct gendisk *disk)
 
 	q->root_blkg = NULL;
 	spin_unlock_irq(&q->queue_lock);
+	mutex_unlock(&q->blkcg_mutex);
 
 	wake_up_var(&q->root_blkg);
 }
-- 
2.51.0