Re: [syzbot] [block?] [trace?] INFO: task hung in blk_trace_ioctl

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Subject: [block?] [trace?] INFO: task hung in blk_trace_ioctl
Author: eadavis@xxxxxx

please test task hung in blk_trace_ioctl

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 8c9660f65153

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index d5d94510af..54ade89a1a 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -588,8 +588,10 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	debugfs_create_file("dropped", 0444, dir, bt, &blk_dropped_fops);
 	debugfs_create_file("msg", 0222, dir, bt, &blk_msg_fops);
 
+	mutex_unlock(&q->debugfs_mutex);
 	bt->rchan = relay_open("trace", dir, buts->buf_size,
 				buts->buf_nr, &blk_relay_callbacks, bt);
+	mutex_lock(&q->debugfs_mutex);
 	if (!bt->rchan)
 		goto err;