From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-124.freemail.mail.aliyun.com (out30-124.freemail.mail.aliyun.com [115.124.30.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 87E621D5CC9 for ; Wed, 2 Sep 2026 03:28:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788319728; cv=none; b=orVgBLYZ8tTGc9axWVlZuFsOI0QfSbDjazcO7BIkhXHueGm9vEmv55DriQ2dZGQY23vSwuuRb0najrmbJTHT/e5UQg00UNNymbBdjCfGf1OAhfr8FobmiZv8X2h1j9TH/+DcGt77G0W5uaLYQ4aiXbIm7kVJSipMUIKE+fSF0KE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788319728; c=relaxed/simple; bh=qmHbCocGqHmOK5vvt1uRHmo/+hbpUJ2fKhhRlroXv3M=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=qWye4GwM4kL2yfayBwnlaCWE71mEXEaSu92RfplidEuZD87LrXsCm21Cj71IaYlqccGnMBzTIeOppSpUeA5DPiR9/QTXcd6/VusgX0RFO5T1gFYhP5B3TuHTfM+bmFXYMbD5v6kr5X9x9A7IwDXjty9BKFnyywlTyI2SuxQdDtQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=jciDB06X; arc=none smtp.client-ip=115.124.30.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="jciDB06X" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1788319723; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=pMvIKLAGFtBlf8v0ZL0jUkwTBxIKdH+TsX1qwT3x62w=; b=jciDB06XBViAdt9cHnHT1o69SfhYujgcGby7qdl/8JlTaVvEuuk1YhQf35ZjyTlMqZojz1evNCc/XnW55yjhHL79pL7lWw4qyCTna4mAihKxtDFW6c5oKtgzfKN3DL4v/Wmgf2JDy+ytzwyK01irsBQtTab0LpYdpCP7ZliaWY4= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033045133197;MF=qinyuntan@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0XAB4RlG_1788319721; Received: from banye.tbsite.net(mailfrom:qinyuntan@linux.alibaba.com fp:SMTPD_---0XAB4RlG_1788319721 cluster:ay36) by smtp.aliyun-inc.com; Wed, 02 Sep 2026 11:28:42 +0800 From: Qinyun Tan To: Andrew Morton Cc: Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Baolin Wang , Xunlei Pang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qinyun Tan Subject: [PATCH] mm/list_lru: disable memcg awareness under cgroup_disable=memory Date: Wed, 2 Sep 2026 11:28:40 +0800 Message-ID: <20260902032840.30250-1-qinyuntan@linux.alibaba.com> X-Mailer: git-send-email 2.43.7 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit __list_lru_init() only collapses a memcg-aware list_lru into plain per-node lists when kmem accounting is disabled (cgroup.memory=nokmem). When the memory controller is disabled entirely (cgroup_disable=memory), mem_cgroup_kmem_disabled() is false, so the lru stays memcg aware even though no object will ever be charged to a memcg. This is more than a semantic inconsistency. folio_memcg_list_lru_alloc() trusts list_lru_memcg_aware() and dereferences the folio's memcg, which is always NULL with the controller disabled. The only mainline caller, folio_memcg_alloc_deferred(), papers over this with an explicit mem_cgroup_disabled() check. The shmem unused-huge shrinker conversion ("mm: shmem: make unused huge shrinker memcg aware") adds a second caller without such a guard, so booting with cgroup_disable=memory and writing to a huge=always tmpfs oopses: BUG: unable to handle page fault for address: 0000000000000488 RIP: 0010:folio_memcg_list_lru_alloc+0x41/0xf0 Call Trace: shmem_get_folio_gfp+0x1cd/0x7c0 shmem_write_begin+0x5d/0x100 generic_perform_write+0x89/0x2a0 shmem_file_write_iter+0x82/0x90 vfs_write+0x256/0x410 ksys_write+0x61/0xe0 do_syscall_64+0x8d/0x460 entry_SYSCALL_64_after_hwframe+0x76/0x7e The faulting address is the offset of mem_cgroup->kmemcg_id, dereferenced on a NULL memcg in memcg_list_lru_allocated(): folio_memcg_list_lru_alloc() list_lru_memcg_aware() <- true, only nokmem checked memcg = folio_memcg(folio) <- NULL memcg_list_lru_allocated(memcg, lru) memcg->kmemcg_id <- NULL pointer dereference Check mem_cgroup_disabled() in __list_lru_init() so that all list_lrus fall back to plain per-node lists when the controller is disabled, matching what the shrinker side already does (shrinker_memcg_alloc() bails out on mem_cgroup_disabled()). This makes the mem_cgroup_disabled() check in callers unnecessary rather than mandatory. Signed-off-by: Qinyun Tan --- Applies on top of mm-new. No Fixes: tag since the commit that makes the crash reachable ("mm: shmem: make unused huge shrinker memcg aware") is only in mm-new; no stable backport is needed either. Reproducer, on mm-new booted with cgroup_disable=memory (CONFIG_MEMCG=y, CONFIG_TRANSPARENT_HUGEPAGE=y): # mount -t tmpfs -o huge=always tmpfs /mnt # echo x > /mnt/f Without this patch the write oopses immediately as shown above: the freshly allocated huge folio extends beyond i_size, so shmem_get_folio_gfp() queues the inode via shmem_unused_huge_add() -> folio_memcg_list_lru_alloc(), which dereferences the NULL folio_memcg(). With this patch the same steps run cleanly: the lru falls back to plain per-node lists and folio_memcg_list_lru_alloc() returns early. >From code inspection the rest of the shmem path handles the NULL objcg fine (obj_cgroup_memcg() and obj_cgroup_put() are NULL-safe, and list_lru_add() with a NULL memcg lands on the per-node list), but I have not exercised the shrinker reclaim itself under cgroup_disable=memory. Discussion: https://lore.kernel.org/linux-mm/20260901115104.2944996-1-qinyuntan@linux.alibaba.com/ mm/list_lru.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/mm/list_lru.c b/mm/list_lru.c index 36662d02ff963..f8be119351cca 100644 --- a/mm/list_lru.c +++ b/mm/list_lru.c @@ -671,7 +671,12 @@ int __list_lru_init(struct list_lru *lru, bool memcg_aware, struct shrinker *shr else lru->shrinker_id = -1; - if (mem_cgroup_kmem_disabled()) + /* + * With the memory controller disabled entirely, no object is ever + * charged to a memcg, so collapse to plain per-node lists just + * like under nokmem. + */ + if (mem_cgroup_disabled() || mem_cgroup_kmem_disabled()) memcg_aware = false; #endif -- 2.43.7