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

[syzbot <syzbot+ed812ed461471ab17a0c@syzkaller.appspotmail.com>]

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Subject: [block?] [trace?] INFO: task hung in blk_trace_ioctl
Author: eadavis@qq.com

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 54ade89a1ad2..f5d3576ef3ed 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -735,7 +735,10 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
 	int ret, start = 0;
 	char b[BDEVNAME_SIZE];
 
-	mutex_lock(&q->debugfs_mutex);
+	if (cmd == BLKTRACESETUP)
+		mutex_lock(&q->debugfs_mutex);
+	else
+		mutex_lock_nested(&q->debugfs_mutex, 2);
 
 	switch (cmd) {
 	case BLKTRACESETUP: