fail_function: Remove a redundant mutex unlock

stable inclusion
from linux-4.19.160
commit 730b192ad262545a269483609f52d29bff503507

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

[ Upstream commit 2801a5da ]

Fix a mutex_unlock() issue where before copy_from_user() is
not called mutex_locked.

Fixes: 4b1a29a7 ("error-injection: Support fault injection framework")
Reported-by: NHulk Robot <hulkci@huawei.com>
Signed-off-by: NLuo Meng <luomeng12@huawei.com>
Signed-off-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NAlexei Starovoitov <ast@kernel.org>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/bpf/160570737118.263807.8358435412898356284.stgit@devnote2Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

kernel/fail_function.c

@@ -261,7 +261,7 @@ static ssize_t fei_write(struct file *file, const char __user *buffer,
 
 	if (copy_from_user(buf, buffer, count)) {
 		ret = -EFAULT;
-		goto out;
+		goto out_free;
 	}
 	buf[count] = '\0';
 	sym = strstrip(buf);
@@ -315,8 +315,9 @@ static ssize_t fei_write(struct file *file, const char __user *buffer,
 		ret = count;
 	}
 out:
-	kfree(buf);
 	mutex_unlock(&fei_lock);
+out_free:
+	kfree(buf);
 	return ret;
 }