linux-kernel - Re: [syzbot] [block?] [trace?] INFO: task hung in blk_trace

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Date: Wed, 31 Jan 2024 09:04:14 +0800
From: Edward Adam Davis <eadavis@...com>
To: syzbot+2373f6be3e6de4f92562@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [block?] [trace?] INFO: task hung in blk_trace_remove (2)

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..5eecdf9b8570 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -330,6 +330,13 @@ static void blk_trace_free(struct request_queue *q, struct blk_trace *bt)
 	kfree(bt);
 }
 
+static void blk_trace_free_rcu(struct blk_trace *bt)
+{
+	free_percpu(bt->sequence);
+	free_percpu(bt->msg_data);
+	kfree(bt);
+}
+
 static void get_probe_ref(void)
 {
 	mutex_lock(&blk_probe_mutex);
@@ -377,12 +384,32 @@ 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_rcu(bt);
+	}
+}
+
 static void blk_trace_cleanup(struct request_queue *q, struct blk_trace *bt)
 {
 	blk_trace_stop(bt);
-	synchronize_rcu();
-	blk_trace_free(q, bt);
+	relay_close(bt->rchan);
+	/*
+	 * If 'bt->dir' is not set, then both 'dropped' and 'msg' are created
+	 * 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);
+	} else {
+		debugfs_remove(bt->dir);
+	}
 	put_probe_ref();
+	call_rcu(&bt->rcu, blk_trace_rcu_free);
 }
 
 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..5f927328b7e6 100644
--- a/include/linux/blktrace_api.h
+++ b/include/linux/blktrace_api.h
@@ -26,6 +26,7 @@ struct blk_trace {
 	struct dentry *dir;
 	struct list_head running_list;
 	atomic_t dropped;
+	struct rcu_head rcu;
 };
 
 extern int blk_trace_ioctl(struct block_device *, unsigned, char __user *);