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Tue, 14 Apr 2026 12:16:02 -0700 (PDT) MIME-Version: 1.0 References: <20260414065206.3236176-1-arnd@kernel.org> In-Reply-To: <20260414065206.3236176-1-arnd@kernel.org> From: Axel Rasmussen Date: Tue, 14 Apr 2026 12:15:25 -0700 X-Gm-Features: AQROBzBC6Y0qvWaUs1yl7ge9ovqyfv4vIoLNfWuOl8c-QyyjXjHVF53HP06oYnA Message-ID: Subject: Re: [PATCH] [v2] mm/vmscan: avoid false-positive -Wuninitialized warning To: Arnd Bergmann Cc: Andrew Morton , Johannes Weiner , Arnd Bergmann , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Yuanchu Xie , Wei Xu , David Hildenbrand , Michal Hocko , Lorenzo Stoakes , Muchun Song , Baolin Wang , Davidlohr Bueso , Koichiro Den , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: BCE5E140013 X-Stat-Signature: 9uqwhw6gesej8cobbsyii73ykkmcnwux X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1776194164-770505 X-HE-Meta: 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 Q6+g5d/5 3gF4SvX5Qjx4HARin2884t57ACmurB4G0XtijXkjWA9LkLmcUZ5LD+C/mmZZYl3AWiVdLu6AKN2vlWeu53GimO7U9EUfIRLv0IA7L91qM75tVKSMjDuJUSPGPHC5LXfK007pYRHxPUmL6DtS89Hw5eF/NUiMp+8rtOTHDezt8m1wOlFSP+6StsY7MpNOh81QUNI+iw1f7z0qRWtSB5MlXeymC+vbnAj7Gh5E7q2Vzl5tz5L0gHkWMZZituGZl/XPuR/GJHJbwoaM8p27fRtrFBeU+8PscWKCJVyi/1ijwVjssRfF03ZxRH2Ru9g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Apr 13, 2026 at 11:52=E2=80=AFPM Arnd Bergmann wr= ote: > > From: Arnd Bergmann > > When the -fsanitize=3Dbounds 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= =3Duninitialized] > > Part of the problem seems to be that read_ctrl_pos() has unusual calling > conventions since commit 37a260870f2c ("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/CAJHvVcjtFW86o5FoQC8MMEXCHAC0FviggaQsd5= EmiCHP+1fBpg@mail.gmail.com/ > Signed-off-by: Arnd Bergmann Reviewed-by: Axel Rasmussen > --- > v2: replace the earlier more invasive cleanup with a trivial > workaround > --- > mm/vmscan.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index d3312c51f3f2..f829435d2807 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -4760,7 +4760,7 @@ static int scan_folios(unsigned long nr_to_scan, st= ruct lruvec *lruvec, > static int get_tier_idx(struct lruvec *lruvec, int type) > { > int tier; > - struct ctrl_pos sp, pv; > + struct ctrl_pos sp, pv =3D {}; > > /* > * 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 =3D {}; > > if (swappiness <=3D MIN_SWAPPINESS + 1) > return LRU_GEN_FILE; > -- > 2.39.5 >