Re: [syzbot] [block?] [trace?] INFO: task hung in blk_trace_remove (2)

[Edward Adam Davis]

please test task hung in blk_trace_remove

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index d5d94510afd3..ce5a1ed01d64 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -320,14 +320,16 @@ static void blk_trace_free(struct request_queue *q, struct blk_trace *bt)
 	 * under 'q->debugfs_dir', thus lookup and remove them.
 	 */
 	if (!bt->dir) {
-		debugfs_lookup_and_remove("dropped", q->debugfs_dir);
-		debugfs_lookup_and_remove("msg", q->debugfs_dir);
+		struct dentry *debugfs_dir = q ? q->debugfs_dir : bt->debugfs_dir;
+
+		debugfs_lookup_and_remove("dropped", debugfs_dir);
+		debugfs_lookup_and_remove("msg", debugfs_dir);
 	} else {
 		debugfs_remove(bt->dir);
 	}
 	free_percpu(bt->sequence);
 	free_percpu(bt->msg_data);
-	kfree(bt);
+	kfree_rcu(bt);
 }
 
 static void get_probe_ref(void)
@@ -377,12 +379,25 @@ static int blk_trace_stop(struct blk_trace *bt)
 	return 0;
 }
 
+static void blk_trace_rcu_free(struct rcu_head *rcu)
+{
+	struct blk_trace *bt;
+
+	bt = container_of(rcu, struct blk_trace, rcu);
+	if (bt) {
+		blk_trace_free(NULL, bt);
+		put_probe_ref();
+	}
+}
+
 static void blk_trace_cleanup(struct request_queue *q, struct blk_trace *bt)
 {
 	blk_trace_stop(bt);
-	synchronize_rcu();
-	blk_trace_free(q, bt);
-	put_probe_ref();
+	if (!bt->dir)
+		bt->debugfs_dir = q->debugfs_dir;
+	mutex_unlock(&q->debugfs_mutex);
+	call_rcu(&bt->rcu, blk_trace_rcu_free);
+	mutex_lock(&q->debugfs_mutex);
 }
 
 static int __blk_trace_remove(struct request_queue *q)
diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
index 122c62e561fc..4920c201bd12 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h
@@ -26,6 +26,8 @@ struct blk_trace {
 	struct dentry *dir;
 	struct list_head running_list;
 	atomic_t dropped;
+	struct dentry  *debugfs_dir;
+	struct rcu_head rcu;
 };
 
 extern int blk_trace_ioctl(struct block_device *, unsigned, char __user *);