From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-75.mta0.migadu.com [91.218.175.75]) (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 F14D846D2D3 for ; Wed, 2 Sep 2026 11:34:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.75 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788348889; cv=none; b=kiam4gA+caPVlQeXQyye/oaSTgsq5iOKGlgL5vQeR7ZkWCutN8uyvGpvAAl7MvYe9Z/gOTLMyoX/HtWgZ15pwvPHKTl50NLpdlPTqHDAMIuF1mI0jlTKICvMhS34rW4xv48F5OpfOOgzyDB5Ko48cbBvcHbQSwNmz9qmtdcxeuI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788348889; c=relaxed/simple; bh=qjw5gpQggZH5kMdGCrNH15qunf+SR8sJSyM7R3/MV2c=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Ufa44RckmMBuvyN3qqZP3TQUOTHza9YOftWRKxNvNyKqd4C+Mwu0WNyg4bWF4pyEqWKAn1aTIDVuU9ri7ToOTwMvx+2nv/E1tLPm8kUhbjJipaRjEfVuciXXMXcyvS2M1VemMNCm14ysLHisqMDek+j1VNKIKGTS6Np0udCCKwM= 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=cGbEubHa; arc=none smtp.client-ip=91.218.175.75 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="cGbEubHa" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=qjw5gpQggZH5kMdGCrNH15qunf+SR8sJSyM7R3/MV2c=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1788348878; v=1; x=1788953678; b=cGbEubHadqfrVll+7NNtWQIYnPU686kaQlFqGD/JIMkOVW5ieqSumYnRxe7b8rcwbG4Iy3Oo ANgS2U+7SDLV1BWt0vhTI4YP1DYyfGKEy6pX3btbTHmpEAPOkc0XC2m8ZbEZs5R9BRUcZP8W2jC MLNZIDIJAoaryukC8TxW+woc= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id 0649d5faa369876e; Wed, 02 Sep 2026 11:34:38 +0000 X-Mizu-Trace-ID: 0649d5faa369876e X-Migadu-Flow: FLOW_OUT Message-ID: <5753d853-df04-4918-9852-c23842c66428@linux.dev> Date: Wed, 2 Sep 2026 12:34:38 +0100 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: Jiayuan Chen , 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> Content-Language: en-US From: Usama Arif In-Reply-To: <20260902073800.305481-1-jiayuan.chen@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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()?