Re: gcc-8: mm/swapfile.c:863:40: error: array subscript 1 is above array bounds of 'struct list_head[1]' [-Werror=array-bounds]

[Kairui Song <ryncsn@gmail.com>]

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On Mon, Aug 19, 2024 at 6:16 PM Naresh Kamboju
<naresh.kamboju@linaro.org> wrote:
>
> On Mon, 19 Aug 2024 at 13:58, Naresh Kamboju <naresh.kamboju@linaro.org> wrote:
> >
> > The x86 builds failed with gcc-8 due to following build warnings / errors on
> > Linux next-20240802 to next-20240819.
> >
> > x86_64 defconfig gcc-8 build failed
> > x86_64 defconfig gcc-13 build pass
> >
> > First seen on the next-20240802 tag.
> >
> >   GOOD: next-20240730
> >   BAD:  next-20240802
>
> Anders bisected this and found the first bad commit id as,
> aded4352f648 ("mm: swap: separate SSD allocation from
> scan_swap_map_slots()") first faulty one
>
> - Naresh
>

Hi Naresh,

Thanks for the report, the problem will occur when CONFIG_THP_SWAP is
disabled. Can you try the following patch? I can confirm it's fixed
with my test.

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From 89f0aafa03ad5878e8902e07e12ec0c020dba2df Mon Sep 17 00:00:00 2001
From: Kairui Song <kasong@tencent.com>
Date: Mon, 19 Aug 2024 19:31:55 +0800
Subject: [PATCH] mm: swap: fix array-bounds error with CONFIG_THP_SWAP=n

Signed-off-by: Kairui Song <kasong@tencent.com>
---
 mm/swapfile.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index d9cf31b04db3..16ec6b7df198 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -836,7 +836,7 @@ static unsigned long cluster_alloc_swap_entry(struct swap_info_struct *si, int o
 		goto done;
 
 	/* Order 0 stealing from higher order */
-	for (int o = 1; o < PMD_ORDER; o++) {
+	for (int o = 1; o < SWAP_NR_ORDERS; o++) {
 		/*
 		 * Clusters here have at least one usable slots and can't fail order 0
 		 * allocation, but reclaim may drop si->lock and race with another user.
-- 
2.45.2