block: fix null-deref in percpu_ref_put

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5N162
CVE: NA

--------------------------------

In the use of q_usage_counter of request_queue, blk_cleanup_queue using
"wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter))"
to wait q_usage_counter becoming zero. however, if the q_usage_counter
becoming zero quickly, and percpu_ref_exit will execute and ref->data
will be freed, maybe another process will cause a null-defef problem
like below:

	CPU0                             CPU1
blk_cleanup_queue
 blk_freeze_queue
  blk_mq_freeze_queue_wait
				scsi_end_request
				 percpu_ref_get
				 ...
				 percpu_ref_put
				  atomic_long_sub_and_test
  percpu_ref_exit
   ref->data -> NULL
   				   ref->data->release(ref) -> null-deref

Fix it by setting flag(QUEUE_FLAG_USAGE_COUNT_SYNC) to add synchronization
mechanism, when ref->data->release is called, the flag will be setted,
and the "wait_event" in blk_mq_freeze_queue_wait must wait flag becoming
true as well, which will limit percpu_ref_exit to execute ahead of time.
Signed-off-by: NZhang Wensheng <zhangwensheng5@huawei.com>
Reviewed-by: NYu Kuai <yukuai3@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

block/blk-core.c

@@ -385,7 +385,8 @@ void blk_cleanup_queue(struct request_queue *q)
 	 * prevent that blk_mq_run_hw_queues() accesses the hardware queues
 	 * after draining finished.
 	 */
-	blk_freeze_queue(q);
+	blk_freeze_queue_start(q);
+	blk_mq_freeze_queue_wait_sync(q);
 
 	rq_qos_exit(q);
 
@@ -502,6 +503,7 @@ static void blk_queue_usage_counter_release(struct percpu_ref *ref)
 	struct request_queue *q =
 		container_of(ref, struct request_queue, q_usage_counter);
 
+	blk_queue_flag_set(QUEUE_FLAG_USAGE_COUNT_SYNC, q);
 	wake_up_all(&q->mq_freeze_wq);
 }
 

block/blk-mq.c

@@ -193,6 +193,7 @@ void blk_freeze_queue_start(struct request_queue *q)
 {
 	mutex_lock(&q->mq_freeze_lock);
 	if (++q->mq_freeze_depth == 1) {
+		blk_queue_flag_clear(QUEUE_FLAG_USAGE_COUNT_SYNC, q);
 		percpu_ref_kill(&q->q_usage_counter);
 		mutex_unlock(&q->mq_freeze_lock);
 		if (queue_is_mq(q))
@@ -203,6 +204,12 @@ void blk_freeze_queue_start(struct request_queue *q)
 }
 EXPORT_SYMBOL_GPL(blk_freeze_queue_start);
 
+void blk_mq_freeze_queue_wait_sync(struct request_queue *q)
+{
+	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter) &&
+			test_bit(QUEUE_FLAG_USAGE_COUNT_SYNC, &q->queue_flags));
+}
+
 void blk_mq_freeze_queue_wait(struct request_queue *q)
 {
 	wait_event(q->mq_freeze_wq, percpu_ref_is_zero(&q->q_usage_counter));

include/linux/blk-mq.h

@@ -574,6 +574,7 @@ void blk_mq_freeze_queue(struct request_queue *q);
 void blk_mq_unfreeze_queue(struct request_queue *q);
 void blk_freeze_queue_start(struct request_queue *q);
 void blk_mq_freeze_queue_wait(struct request_queue *q);
+void blk_mq_freeze_queue_wait_sync(struct request_queue *q);
 int blk_mq_freeze_queue_wait_timeout(struct request_queue *q,
 				     unsigned long timeout);
 

include/linux/blkdev.h

@@ -643,6 +643,8 @@ struct request_queue {
 #define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */
 /*at least one blk-mq hctx can't get driver tag */
 #define QUEUE_FLAG_HCTX_WAIT	30
+/* sync for q_usage_counter */
+#define QUEUE_FLAG_USAGE_COUNT_SYNC    31
 
 #define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
 				 (1 << QUEUE_FLAG_SAME_COMP) |		\