[PATCH 2/5] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex

[Yu Kuai]

bfq_end_wr_async() iterates q->blkg_list while only holding bfqd->lock,
but not blkcg_mutex. This can race with blkg_free_workfn() that removes
blkgs from the list while holding blkcg_mutex.

Add blkcg_mutex protection in bfq_end_wr() before taking bfqd->lock to
ensure proper synchronization when iterating q->blkg_list.

Signed-off-by: Yu Kuai <yukuai@xxxxxxx>
---
 block/bfq-cgroup.c  | 3 ++-
 block/bfq-iosched.c | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 37ab70930c8d..f765e767d36a 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -939,11 +939,12 @@ void bfq_end_wr_async(struct bfq_data *bfqd)
 	struct blkcg_gq *blkg;
 
 	list_for_each_entry(blkg, &bfqd->queue->blkg_list, q_node) {
 		struct bfq_group *bfqg = blkg_to_bfqg(blkg);
 
-		bfq_end_wr_async_queues(bfqd, bfqg);
+		if (bfqg)
+			bfq_end_wr_async_queues(bfqd, bfqg);
 	}
 	bfq_end_wr_async_queues(bfqd, bfqd->root_group);
 }
 
 static int bfq_io_show_weight_legacy(struct seq_file *sf, void *v)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 141c602d5e85..42ccfd0c6140 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2643,10 +2643,13 @@ void bfq_end_wr_async_queues(struct bfq_data *bfqd,
 static void bfq_end_wr(struct bfq_data *bfqd)
 {
 	struct bfq_queue *bfqq;
 	int i;
 
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	mutex_lock(&bfqd->queue->blkcg_mutex);
+#endif
 	spin_lock_irq(&bfqd->lock);
 
 	for (i = 0; i < bfqd->num_actuators; i++) {
 		list_for_each_entry(bfqq, &bfqd->active_list[i], bfqq_list)
 			bfq_bfqq_end_wr(bfqq);
@@ -2654,10 +2657,13 @@ static void bfq_end_wr(struct bfq_data *bfqd)
 	list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
 		bfq_bfqq_end_wr(bfqq);
 	bfq_end_wr_async(bfqd);
 
 	spin_unlock_irq(&bfqd->lock);
+#ifdef CONFIG_BFQ_GROUP_IOSCHED
+	mutex_unlock(&bfqd->queue->blkcg_mutex);
+#endif
 }
 
 static sector_t bfq_io_struct_pos(void *io_struct, bool request)
 {
 	if (request)
-- 
2.51.0