From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f176.google.com (mail-yw1-f176.google.com [209.85.128.176]) (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 3865D4432FD for ; Thu, 27 Aug 2026 14:59:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787842762; cv=none; b=M7pbtc3k7e1yhCFcgRSO/vYKzs7IwBNtXMwcWxLKJqfXJrFvLyJnFc3eiAy4YGaFg3UZCJPvBBoEKPNJQ3B1qXLvA7/SPFfNaQnfZ22uvzSjb3Z6enyC1V+QmK2nxxPn+pMYQ19RQhCAQgabZbEFUV4qG17nhKllWJtN0LikGK8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787842762; c=relaxed/simple; bh=RR+IUy6BeU23gJRdnSXxRw8SirU1x2z1Zv0XN+mlf+c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=adIADVqjo3xPlLEhJg2LP0UtOU5wX3+fDQagWiZnG8Nv768ugmHUgC71OhnpqUJwCkkd87U4VhGkHBdslJ/zN8wKvOayZDI16jVGDh9vFznJTDJf/RTH2nTnPwQBygmF+HF54FZ2VXXrRpJujBxqJ+3E9jtikq+iT7iigValsEU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=cmpxchg.org; spf=pass smtp.mailfrom=cmpxchg.org; dkim=pass (2048-bit key) header.d=cmpxchg.org header.i=@cmpxchg.org header.b=lFoZFqjD; arc=none smtp.client-ip=209.85.128.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=cmpxchg.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=cmpxchg.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=cmpxchg.org header.i=@cmpxchg.org header.b="lFoZFqjD" Received: by mail-yw1-f176.google.com with SMTP id 00721157ae682-8565d77c277so36846507b3.0 for ; Thu, 27 Aug 2026 07:59:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg.org; s=google; t=1787842759; x=1788447559; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=d4lPcSEVrhw95aM0IABtxJRmbb0KihXHWFn9jTHO+gA=; b=lFoZFqjDq9phDt72Un3JCDMdeZIOtIYGQ3jWW4EYhWYAo5CbPp0QcKiOnE+AJbaaYq AYjewtTUfh+eGHC5p6ImFm9/Suxn0PAei/84jTYezOcu6QW30E9jfACTJl3odUB/rzki mXWCYw1x4fZuy+MmpstiAfGk3sl6X36ssgJwW9lsGhJpoSk7uYIXCAHFGb1ng5Cc6NTt Zts2ACxDcGj2hFRNU3hH5dnRzXIo5r+odb8Gmqkw55/zT0jn53Io4y5DmActQiBp2s0b lQ6r9IjvBlj1GWtJt1uv0b+KMPvK7WieOrL7WAbrIMcYwe2XgIao6ZCexzg2yfuP6uBD svRQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787842759; x=1788447559; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=d4lPcSEVrhw95aM0IABtxJRmbb0KihXHWFn9jTHO+gA=; b=osBs++B0AU8SqCGhFATMiNcNVm5+x5SLuuxBKffIrCs3VCeiUsV3o2FuBVs3vhmAT2 a4eNAWADw1X+2jNFlsa3H0MVM+j2ORfUUZ6HYGVY37tHSsHgVtvxVuOqWxdpcbs2tY42 7X4/bh5xIYCSn4S4pMoWOR5Rq5B3242sWvY485awt0KYxElDm0ecoZuODH8bQvW/fcZd Oe0MX2Y+hybF6BNFU7WsPmaXm9s5RP4nx3ofaEUJJBGOOu+u6DiSMhKnqRGvoQRkVBhI 7XiZMAaLRYbGEdFhCNWGl29GPcgrUIV3b4H7n/+6exilu1P/gsgR/M/+kP7uSmdj3O1R G+jw== X-Forwarded-Encrypted: i=1; AHgh+Rp1kcCK+PEp9g7JLEZDrBYHY5a/qSq8P0HsM/gd6yAqMa5/oQGGb5IYrymBjAIqeueZPeHkx/6rLbztWJA=@vger.kernel.org X-Gm-Message-State: AFuF++m5iDsvvXR5pZ2rUUfhSUev5mwA1rVJPfCF49o6gfJ7k+UqwR/h ZX9kocI+lHZ4aLI7jQgxPd0RX2hfwEBVFLnAp9hKaM06wLyMMmp8uBVTA/km3MT9y3Q= X-Gm-Gg: AR+sD13y5k9EZZh8EW0kHhaZjrr/Xlstu0Y+eTrSaLLPMeSBxgK3EMJpuW8uypf3LLD MkqAbtfvwx+IzPQiePhT7n80meica2LlGghFYdj60hf1qEcj6DHHwO/2qZu/0GW7+8qolcP2hw1 FDPzww14LML5ixbMzljbDzj2aRYqBe1aWLJIBLjDU6VPRg3MApFUSxB9aGjQy3izI0CeZg8C26E vMNZ78rECJdi3gO0RqutJt3Ijxr/4aOPVp09mxjwFipILwXFLBENlFgitQso9LIy5hH3fDsdygb m0xp/3ePv3aUYBd/XM4qqXTPhS31QgCfYnIVB1o2doNrJq3e4Wyic3a26GMqcImnmu+2PVcYT+P g5u9qNms9/vK4IG3ebxzJIQGjfK0Q142QzVOEAyNnRyZTsfysXoFJcilLYA2oNOE3KkOQ+G9tOD JD79X4i/rQRBvlxPvmL1ryNjXkwgK7M5BbdNFLk8jNf81aXA0vR1cCVJa+8sQ/ X-Received: by 2002:a05:690c:e288:10b0:858:def3:3422 with SMTP id 00721157ae682-858def3356cmr38360687b3.27.1787842759108; Thu, 27 Aug 2026 07:59:19 -0700 (PDT) Received: from localhost ([2605:8600:200:1a83:fe59:7385:2855:8588]) by smtp.gmail.com with ESMTPSA id 00721157ae682-85b5bc34efasm11365667b3.7.2026.08.27.07.59.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Aug 2026 07:59:18 -0700 (PDT) Date: Thu, 27 Aug 2026 10:59:17 -0400 From: Johannes Weiner To: Jiayuan Chen Cc: linux-mm@kvack.org, stable@vger.kernel.org, syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com, Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Yosry Ahmed , Chris Li , Jens Axboe , Jan Kara , Tejun Heo , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memcontrol: fix data-race on reading jiffies_64 Message-ID: <20260827145917.GB3004@cmpxchg.org> References: <20260827025457.116191-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260827025457.116191-1-jiayuan.chen@linux.dev> On Thu, Aug 27, 2026 at 10:54:56AM +0800, Jiayuan Chen wrote: > KCSAN reported a data-race between tick_do_update_jiffies64() updating > jiffies_64 and mem_cgroup_flush_stats_ratelimited() reading it directly. > > Unlike jiffies, jiffies_64 is not volatile, so raw reads are plain > accesses and can even be torn on 32-bit. Use get_jiffies_64() instead, > and fix the same pattern in mem_cgroup_flush_foreign(). > > Cc: > Fixes: 508bed884767 ("mm: memcg: change flush_next_time to flush_last_time") > Fixes: 97b27821b485 ("writeback, memcg: Implement foreign dirty flushing") > Reported-by: syzbot+ced4d9a8cadb5ef3adae@syzkaller.appspotmail.com > Signed-off-by: Jiayuan Chen Acked-by: Johannes Weiner Minor nit: > @@ -785,7 +785,7 @@ void mem_cgroup_flush_stats(struct mem_cgroup *memcg) > void mem_cgroup_flush_stats_ratelimited(struct mem_cgroup *memcg) > { > /* Only flush if the periodic flusher is one full cycle late */ > - if (time_after64(jiffies_64, READ_ONCE(flush_last_time) + 2*FLUSH_TIME)) > + if (time_after64(get_jiffies_64(), READ_ONCE(flush_last_time) + 2 * FLUSH_TIME)) > mem_cgroup_flush_stats(memcg); time_is_after_jiffies64()