mm/pin_mem: add invalid check for pinmemory boot parameter

euleros inclusion
category: feature
bugzilla:https://gitee.com/openeuler/kernel/issues/I4UCEQ
CVE: NA

------------
When the pinmemory setting string is null, return directly
without setting pinmemory addr.
Signed-off-by: NJingxian He <hejingxian@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

mm/pin_mem.c

@@ -1092,9 +1092,12 @@ static int __init parse_pin_memory(char *cmdline)
 {
 	char *cur = cmdline;
 
+	if (!cmdline)
+		return 0;
+
 	pin_mem_len = memparse(cmdline, &cur);
 	if (cmdline == cur) {
-		pr_warn("crashkernel: memory value expected\n");
+		pr_warn("pinmem: memory value expected\n");
 		return -EINVAL;
 	}