From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=95.215.58.81 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792635517; b=fjgvOweQ9wcN6Kjm00AkGVadJ2IaCVhZWZLU+TjRYGWUhIpZ4VmOKvKOJya1UdZwN00F FAuvtGNSaaSM/cSj/gurDNcoBolX9OTGjaH6jBjhJQJ84hQHOfiWs2LW0K6HhkkB87dno QGmihfu7t7UftNuPQhXqhtRpFA1crXzz0vKbNImdXuQz5EilMLrvxNnv4z8rWERrE1Zke T8lEhxtADaGzPYd0cpmrbItMOcMVnoJtSbYcSnz/fMjVDXaqU3MboIPdW/OpFMHuPJLN4 bLG1Lh7/ATELEs/TMbFvEorlnia87VJQNwWZNSW7R3wj/IUz5CvRpYZv7WW0SDZASUg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792635517; h=DMARC-Filter:X-Envelope-To:DKIM-Signature:X-Envelope-To:Received: X-Mizu-Trace-ID:X-Migadu-Flow:Content-Type:Mime-Version:Subject:From: In-Reply-To:Date:Cc:Content-Transfer-Encoding:Message-Id:References: To:X-Mailer; bh=5FdXvp0CpV6t+Cak3H9/hip6PpHzjqeJ2F/KsA5v8Bg=; b=bAPQKxwjVodIXFy/cpIzbglvJm5XF2iq9wnpXhTyqkMnjGmszN1FH/iRRrLF2w2n3PKP ZLJ9/866ignv9yoSValtLFiLGZ3f/Rlrn3S7xvYM6JWXfJYJHma2jURH/IPWQp/TkKJDu /xTNjKKPvC31G272Lni2Q6Om9ArAQjlYqZFL0V7CFBEmwO+KWt7CMkE7X0BNsg3EOwKND um656LfnbXpX0nG93WJI111q0Q7xA/dBj/C1Yr8nAkSHB5LHJANENN5cjGArOoxxNcqyg CmgfJYlX7KEm+tKORgKOxJEoruceS2LIpMbH4ctlvkpkSVj+dEVurCE9jj7IhUuj+Ew== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=IBxQWFNP; arc=none smtp.remote-ip=95.215.58.81 Received: from mta1.migadu.com (out-81.mta1.migadu.com [95.215.58.81]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52EA3606A31D for ; Thu, 22 Oct 2026 02:18:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 52EA3606A31D 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, unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=IBxQWFNP X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=MPi9YymNFv5TIm/0npc+3JpMtggtpk/tzZ51y3ItgYU=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1792635514; v=1; x=1793240314; b=IBxQWFNPCvnFrgSk8wNrkI7Oi/n4lRyy9RW2H4ACiAxmQo+skmFBWY2sjZuCvAUumhz1cqSC D19c9ufAOOOr5StR1gJsNJPR3IXEVxdRLOYYRwKOIasZF9J/E9sLrfcmRQY0jjVEbKCnvaVJ231 DA0VtRiikZiT5pSlcn2zXRsk= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta12.migadu.com with ESMTPS id 4b7912ba18c63ef4; Thu, 22 Oct 2026 02:18:34 +0000 X-Mizu-Trace-ID: 4b7912ba18c63ef4 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3901.100.1.1.12\)) Subject: Re: [PATCH] mm/page_counter: use WRITE_ONCE() for emin/elow when parent is the root From: Muchun Song In-Reply-To: <20261021204818.3431099-1-shakeel.butt@linux.dev> Date: Thu, 22 Oct 2026 10:18:17 +0800 Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Chris Down , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Sashiko Content-Transfer-Encoding: quoted-printable Message-Id: References: <20261021204818.3431099-1-shakeel.butt@linux.dev> To: Shakeel Butt X-Mailer: Apple Mail (2.3901.100.1.1.12) > On Oct 22, 2026, at 04:48, Shakeel Butt = wrote: >=20 > page_counter_calculate_protection() runs without locks. Several > reclaimers can update the same counter's emin and elow at the same > time, and readers such as mem_cgroup_below_min(), = mem_cgroup_protection() > and the dmem eviction code load them with READ_ONCE(). >=20 > Commit b3a7822e5e75 ("mm, memcg: prevent mem_cgroup_protected store > tearing") made the main path store emin and elow with WRITE_ONCE(), = but > it missed the early return for a counter whose parent is the reclaim > root. Those two stores are the only plain accesses to emin and elow > left. >=20 > With CONFIG_KCSAN_STRICT=3Dy, a few tasks writing to the same cgroup's > memory.reclaim trigger reports like this within seconds: >=20 > BUG: KCSAN: data-race in page_counter_calculate_protection / = shrink_node >=20 > read (marked) to 0xff1f91b146d40e40 of 8 bytes by task 163 on cpu 4: > shrink_node+0x57a/0x1210 > do_try_to_free_pages+0x194/0x930 > try_to_free_mem_cgroup_pages+0x204/0x3f0 > user_proactive_reclaim+0x28a/0x4d0 > memory_reclaim+0x35/0x50 > ... >=20 > write to 0xff1f91b146d40e40 of 8 bytes by task 167 on cpu 6: > page_counter_calculate_protection+0x1fa/0x360 > mem_cgroup_calculate_protection+0x4e/0x70 > shrink_node+0x53e/0x1210 > ... >=20 > The default KCSAN config does not report it, because it treats aligned > word-sized plain writes as atomic. >=20 > Use WRITE_ONCE() for these two stores as well. >=20 > There is no functional change. Readers already accept stale values, = and > compilers emit a single word-sized store either way: with GCC 14 the > x86-64 object code is the same before and after this change. >=20 > Fixes: b3a7822e5e75 ("mm, memcg: prevent mem_cgroup_protected store = tearing") > Reported-by: Sashiko > Signed-off-by: Shakeel Butt Acked-by: Muchun Song Thanks.