Re: [PATCH] mm/memblock.c: fix NULL dereference error

[zijun_hu <zijun_hu@zoho.com>]

Hi All,

this mail correct the following mistakes in last mail
1, remove test patch attached 
2, format patch to satisfy rules
i am so sorry for my mistake

Hi Andrew,

this patch is part of https://lkml.org/lkml/2016/7/26/347 and isn't merged in
as you advised in another mail, i release this patch against linus's mainline
for fixing relevant bugs completely

>From 5d79c31d755dc3f03ecc5b4134f21793258636cd Mon Sep 17 00:00:00 2001
From: zijun_hu <zijun_hu@htc.com>
Date: Tue, 2 Aug 2016 12:35:28 +0800
Subject: [PATCH] mm/memblock.c: fix NULL dereference error

it causes NULL dereference error and failure to get type_a->regions[0] info
if parameter type_b of __next_mem_range_rev() == NULL

the bugs are fixed by checking before dereferring and initializing idx_b
to 0

the approach is tested by dumping all types of region via
__memblock_dump_all() and __next_mem_range_rev() fixed to UART separately
the result is okay after checking the logs

Signed-off-by: zijun_hu <zijun_hu@htc.com>
Tested-by: zijun_hu <zijun_hu@htc.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
 mm/memblock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index ff5ff3b..250dd48 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -994,7 +994,10 @@ void __init_memblock __next_mem_range_rev(u64 *idx, int nid, ulong flags,
 
 	if (*idx == (u64)ULLONG_MAX) {
 		idx_a = type_a->cnt - 1;
-		idx_b = type_b->cnt;
+		if (type_b != NULL)
+			idx_b = type_b->cnt;
+		else
+			idx_b = 0;
 	}
 
 	for (; idx_a >= 0; idx_a--) {
-- 
1.9.1