pstore: Actually give up during locking failure

Without a return after the pr_err(), dumps will collide when two threads
call pstore_dump() at the same time.

Signed-off-by: Liu Hailong <liuhailong5@huawei.com>
Signed-off-by: Li Pengcheng <lipengcheng8@huawei.com>
Signed-off-by: Li Zhong <lizhong11@hisilicon.com>
[kees: improved commit message]
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 14984d9..60e6db6 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -493,6 +493,7 @@
 		if (!is_locked) {
 			pr_err("pstore dump routine blocked in %s path, may corrupt error record\n"
 				       , in_nmi() ? "NMI" : why);
+			return;
 		}
 	} else {
 		spin_lock_irqsave(&psinfo->buf_lock, flags);