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Wed, 02 Sep 2026 07:38:10 +0000 X-Mizu-Trace-ID: 7b5fe957ff10b172 X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen To: linux-mm@kvack.org Cc: Jiayuan Chen , Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Shakeel Butt , Kairui Song , Johannes Weiner , Usama Arif , linux-kernel@vger.kernel.org Subject: [PATCH] mm/shrinker: fix bogus set_shrinker_bit() with cgroup.memory=nokmem Date: Wed, 2 Sep 2026 15:37:59 +0800 Message-ID: <20260902073800.305481-1-jiayuan.chen@linux.dev> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 1387F40008 X-Stat-Signature: ewuqfxg9m1jzti93bg71fu57rk68i46e X-HE-Tag: 1788334693-307663 X-HE-Meta: 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 hxFTafAP /73jEPSFKKIhc2bo35HBrS4BUqS1ynUxv8QsvM5CfjVGJ30hJiqDZ6lehJIey4Kr3zER2/y/2tQksaYPzi4PIgGK8j+5obB9X/UOrdImTLebAdiMeUOzhJwcoTCM8dyCXb82y5jgRoNrxPjSCV5ZWNCYhwsxsjLkpithdFtyhNdR5cqvuBekxy2LqUUEU7AbwgX2fsyA8CPBBuN9ahU0PDeLH35q9RyAU4P9sDuDeDPlz/ebKWr3/1FmUrd+Z3CD+NARmsP3GPMaEfSYgNNkSfvxucQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: With cgroup.memory=nokmem, shrinker_memcg_alloc() bails out early and never allocates an id, so shrinker->id keeps the 0 it got from the kzalloc() in shrinker_alloc(). __list_lru_init() then copies that 0 into lru->shrinker_id, where it looks like a valid bit index. Nothing calls expand_shrinker_info() on nokmem either, so shrinker_nr_max stays 0 and every memcg ends up with an empty map (map_nr_max == 0). deferred_split_folio() hands a real memcg to __list_lru_add() regardless of whether the lru is memcg aware, so the first THP queued in a cgroup does set_shrinker_bit(memcg, nid, 0) and trips the bounds check: WARNING: mm/shrinker.c:212 at set_shrinker_bit+0x7d/0x90, CPU#126 Call Trace: deferred_split_folio+0x18c/0x220 map_anon_folio_pmd_nopf+0xdd/0x130 map_anon_folio_pmd_pf+0x14/0xb0 do_huge_pmd_anonymous_page+0x1a1/0x620 __handle_mm_fault+0xea9/0x10d0 handle_mm_fault+0xe5/0x320 do_user_addr_fault+0x1cc/0x870 exc_page_fault+0x81/0x1b0 asm_exc_page_fault+0x27/0x30 Harmless, the WARN_ON_ONCE() is what keeps the out of bounds unit[] read from happening, but the id should not look valid in the first place. Clear it before returning. Two other spots could paper over this: drop the id in __list_lru_init() when nokmem turns memcg_aware off, or make deferred_split_folio() pass NULL like list_lru_add_obj() does. Both leave shrinker->id lying around for the next caller, so fix it where the id is handed out. Fixes: fafaeceb89a5 ("mm: switch deferred split shrinker to list_lru") Signed-off-by: Jiayuan Chen --- mm/shrinker.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/shrinker.c b/mm/shrinker.c index a70aab124a0e..7ec2a9704f6f 100644 --- a/mm/shrinker.c +++ b/mm/shrinker.c @@ -227,6 +227,8 @@ static int shrinker_memcg_alloc(struct shrinker *shrinker) { int id; + shrinker->id = -1; + if (mem_cgroup_disabled()) return -ENOSYS; if (mem_cgroup_kmem_disabled() && !(shrinker->flags & SHRINKER_NONSLAB)) -- 2.43.0