From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-46.mta0.migadu.com [91.218.175.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EDF4633BBCF for ; Wed, 2 Sep 2026 07:38:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.46 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788334705; cv=none; b=HAHhZAJoZ/2kPpE3nTQX/voMRz7AFk6QgNH1ROOW80JM12gbPHUixSB77FY7XFYIvkva2/EyGlsdTqTOju64E7/cYRKZkVHd9Bcn2LFs9H2Jh4buuggm5NbOmozIKY3FhjX3sD86XUatuuL0ZJ1BFXbuMKpjgFD77+TlgGYIQj8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788334705; c=relaxed/simple; bh=bWqKM55BsocJ4wzic/HTSDg71D6vbUFl84C/nnmct8E=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=VPPJr7i9/dlttUusvX2h54lszdncDuRy2wAJr8RRZcygxDw00KVtcFzmuxkz/7bw37J9+i5lSssHZC78tzsy4oH4C4JruNh+UDWpXAC5qdkYNH0frElr9kgCqTaSaS9tMpGwFMF9fftO8cmJqaiGn7TFaSSa0H9YPQhxUjMC1LY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=vV6wCO1H; arc=none smtp.client-ip=91.218.175.46 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="vV6wCO1H" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=bWqKM55BsocJ4wzic/HTSDg71D6vbUFl84C/nnmct8E=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788334700; v=1; x=1788939500; b=vV6wCO1H7AdtHnmeMst+X9cfkYqTrExVIzmNGbAHjGYkjidiWQWP4yp3VmZMew/fPJpfyah/ EKFg1DgyBb/TG3ovWtiTl1n7cf9+7qj9qkXU1Dp/Ye+Ij5xU5o7MgcKlLKo1XGCnRrXgQ1CQw/A HicbOyIWAF/J2o9YQMW+Bnd8= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 7b5fe957ff10b172; 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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