From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-42.mta1.migadu.com [95.215.58.42]) (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 B0F3C39FCDB for ; Wed, 2 Sep 2026 11:44:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.42 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788349480; cv=none; b=GsrdKdh3O6NTrFxOkYp7XjeTnKV0PX80HlzXP3Ywn0qQmHY+7n6azAtD+HW3f8nQAx4I6dwVI7Lm/YhsyrWb6ySfe1zSbipDiMPZfohNThJfgCiRFVtQuSeL4XW/KJb841lXtPLNhM5E/lz4i5ytmqHaVYf8xu7kEql6vrB2pUI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788349480; c=relaxed/simple; bh=FQ3fwj4HF3bn+KhRvieo4GqR7LJ+Nrb7IZb14BFcNNo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lqWC6IzZSTR23F4ieYahnCjqBD/Als14VRrb9/JMHnApyObJULdNI2+rSdttnLGCfdjMPmd2rIdmTZPtBNW8YmEoIR+2QXyX7/SV7DXdpTtqdXXaPf2vnPvGfIGfZMJLqW/b1TqUPuqGgcAhp5SMeksIbj09htv13UcoP66tZ9U= 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=IULNUPg0; arc=none smtp.client-ip=95.215.58.42 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="IULNUPg0" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=FQ3fwj4HF3bn+KhRvieo4GqR7LJ+Nrb7IZb14BFcNNo=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788349475; v=1; x=1788954275; b=IULNUPg0nHXswditelk/BOCU+pa3bBLxp5InD7yhF3hLPkFdYMUF89ZLtaeOa4AQ1ITHmLRI 2+Ly92fai4lHHg84v1RdKrxXiGxVUtCuY3toqYfXa/rjScbnzE5/34Lj0sQFEJwH83P57+v1IqO qNR21SzIiED2K3s+MwztcUS4= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 7b46bf04467625a6; Wed, 02 Sep 2026 11:44:35 +0000 X-Mizu-Trace-ID: 7b46bf04467625a6 X-Migadu-Flow: FLOW_OUT Message-ID: <2def1a1a-cb47-4435-bc8a-e787672022ae@linux.dev> Date: Wed, 2 Sep 2026 19:44:23 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/shrinker: fix bogus set_shrinker_bit() with cgroup.memory=nokmem To: Usama Arif , linux-mm@kvack.org Cc: Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Shakeel Butt , Kairui Song , Johannes Weiner , linux-kernel@vger.kernel.org References: <20260902073800.305481-1-jiayuan.chen@linux.dev> <5753d853-df04-4918-9852-c23842c66428@linux.dev> From: Jiayuan Chen In-Reply-To: <5753d853-df04-4918-9852-c23842c66428@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit on 9/2/26 7:34 PM, Usama Arif wrote: > > On 02/09/2026 08:37, 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 >> --- >> 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)) > > Thanks for the fix! > > I think the initialization would look better in shrinker_alloc()? Well, we have to add macro if we move it to shrinker_alloc()     shrinker->flags = flags | SHRINKER_ALLOCATED;     shrinker->seeks = DEFAULT_SEEKS; +#ifdef CONFIG_MEMCG +        shrinker->id = -1; +#endif No strong preference for me :)