[PATCH v3 1/7] blk-cgroup: protect q->blkg_list iteration in blkg_destroy_all() with blkcg_mutex

[Yu Kuai <yukuai@fnnas.com>]

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.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
---
 block/blk-cgroup.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3cffb68ba5d8..0bc7b19399b6 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -574,6 +574,7 @@ 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;
@@ -592,6 +593,7 @@ 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;
 		}
@@ -611,6 +613,7 @@ static void blkg_destroy_all(struct gendisk *disk)
 
 	q->root_blkg = NULL;
 	spin_unlock_irq(&q->queue_lock);
+	mutex_unlock(&q->blkcg_mutex);
 }
 
 static void blkg_iostat_set(struct blkg_iostat *dst, struct blkg_iostat *src)
-- 
2.51.0