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 <[email protected]>
Signed-off-by: Li Pengcheng <[email protected]>
Signed-off-by: Li Zhong <[email protected]>
[kees: improved commit message]
Signed-off-by: Kees Cook <[email protected]>

fs/pstore/platform.c

@@ -493,6 +493,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		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);