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mm/vmscan: avoid false-positive -Wuninitialized warning

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When the -fsanitize=bounds sanitizer is enabled, gcc-16 sometimes runs
into a corner case in the read_ctrl_pos() pos function, where it sees
possible undefined behavior from the 'tier' index overflowing, presumably
in the case that this was called with a negative tier:

In function 'get_tier_idx',
    inlined from 'isolate_folios' at mm/vmscan.c:4671:14:
mm/vmscan.c: In function 'isolate_folios':
mm/vmscan.c:4645:29: error: 'pv.refaulted' is used uninitialized [-Werror=uninitialized]

Part of the problem seems to be that read_ctrl_pos() has unusual calling
conventions since commit 37a260870f ("mm/mglru: rework type selection")
where passing MAX_NR_TIERS makes it accumulate all tiers but passing a
smaller positive number makes it read a single tier instead.

Shut up the warning by adding a fake initialization to the two instances
of this variable that can run into that corner case.

Link: https://lore.kernel.org/all/CAJHvVcjtFW86o5FoQC8MMEXCHAC0FviggaQsd5EmiCHP+1fBpg@mail.gmail.com/
Link: https://lore.kernel.org/20260414065206.3236176-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Koichiro Den <koichiro.den@canonical.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Arnd Bergmann 2026-04-14 08:51:58 +02:00 committed by Andrew Morton
parent e86ffbe7df
commit 3de705a43a
1 changed files with 2 additions and 2 deletions
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4
mm/vmscan.c
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@ -4760,7 +4760,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec,
static int get_tier_idx(struct lruvec *lruvec, int type)
{
int tier;
struct ctrl_pos sp, pv;
struct ctrl_pos sp, pv = {};
/*
* To leave a margin for fluctuations, use a larger gain factor (2:3).
@ -4779,7 +4779,7 @@ static int get_tier_idx(struct lruvec *lruvec, int type)
static int get_type_to_scan(struct lruvec *lruvec, int swappiness)
{
struct ctrl_pos sp, pv;
struct ctrl_pos sp, pv = {};
if (swappiness <= MIN_SWAPPINESS + 1)
return LRU_GEN_FILE;