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Wed, 02 Sep 2026 15:40:12 +0000 X-Mizu-Trace-ID: f8325dd3e3de5b6b X-Migadu-Flow: FLOW_OUT Date: Wed, 2 Sep 2026 08:40:10 -0700 From: Shakeel Butt To: Jiayuan Chen Cc: linux-mm@kvack.org, Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Kairui Song , Johannes Weiner , Usama Arif , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/shrinker: fix bogus set_shrinker_bit() with cgroup.memory=nokmem Message-ID: References: <20260902073800.305481-1-jiayuan.chen@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260902073800.305481-1-jiayuan.chen@linux.dev> X-Stat-Signature: er3566p4ahwnyygswyymhk3q44nsii85 X-Rspamd-Queue-Id: 2299B20007 X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1788363614-382668 X-HE-Meta: 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 E28QiEoY BVtCjwmMhTtwACcn91dAJi6jXK9/q3KA/8Gcf20devHC3TFfjvfaBGppEndOYRy2WbCI4JFTwNb7jQCK8AoAeAkTQGb4cjLNBKkjakyleuHjNEX57HkDPNKFu8q85Uy24Dtcf+BuBcpYYX8wkIdkQtU9ZtN77EC9/Kc2+cZ2iseY13scZz8MXijxKFvYXjE1eG4Qw+4tmJo1QkZBaJSYdXJoJhAiQaxKILEFpS8F8fWCrAqWzMCj1lduIVCZtIA7yh/wpwxLl2PEx5CYIX1uTr7gOGnKJx7lVyQWFDELRdFLSi0PsLPMaUDrNXwOPJcrDhNeQ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 02, 2026 at 03:37:59PM +0800, Jiayuan Chen wrote: > 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 Acked-by: Shakeel Butt