From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f174.google.com (mail-pl1-f174.google.com [209.85.214.174]) (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 CCF3E632 for ; Tue, 23 Jul 2024 06:13:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721715198; cv=none; b=qg1ktdaKIlPjgwkwXiGTB6A8WYUdAO0oBtH3/9ffq+uwZIdripikWmTBB9FO2e5XQWAvqYfYYU66uBuMhgoI9KjiKVFCFfjAwK42DK2JlauoFEVW/iuQSH74n7eEYlwSwdOhLkZTiiIhoq6DucPoKdjjzjSsBepQqBJ3XAHmzk0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721715198; c=relaxed/simple; bh=VQJqynMJxzrsZAD1nG5keT3FGlcpHAyjrPHZQw64PEM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Jz3aHBaslJaxn275YuG3E71ul4rpuk6A0IR50maDWeYB7zN9B2B3rMgR1HO4rAoRfEZXuC9s58gBecu0vsc9sfTYCIMKOxHr5A7Dbg/xD2dUA9H4/GjkA0P6M7ktsz1lmJTfvAC4tvlpJgL92g25skihTui783J50utuBipWPpY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.214.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-pl1-f174.google.com with SMTP id d9443c01a7336-1fb3b7d0d56so25845815ad.1 for ; Mon, 22 Jul 2024 23:13:16 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721715196; x=1722319996; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=veqI8JpWND9x/vrna5uBQjtmH0anUTbMAymlouU2IIA=; b=whQ8YfNeFbBZ7jmstcrRTB1QSI0gZ7oJzMvaeIGsCxHy7iD7MQc88D/t0DmSlo7L8S Ma/LCDfibOQlttlbP8OCTbEQMfvPw0aI5xWkSQJoMk+gTpO3SKRx3BusylKrmY3rfCPx QGMl/J8/+E3hBeKAuJouzWLYSyFBJFFse5jbS2+cHb1+bzuShxVBDDU5J/30BOGPt2zG HLwP2iiyD4l0+f5H7uk0aH6XCDzF7xwJO5u29MwDhDXp/u8VtYHmPNZy6+4T//gIQFQX zyQNm+F2TzwAmCDvNq0/cKfzeXxxhuzNjZUROGvdwd0BsvK0UZiVet/L8V9MZk0IkGd7 QJqA== X-Forwarded-Encrypted: i=1; AJvYcCV/UoQYST6xTjBOgqff8gPIv2d/eTekBnDM4cjjRm1qMvtGCPnU2i6/TK++9SMceH49sxmmD5J6fxQhI1iE0Jl56oPkur2XH9NaB2YS X-Gm-Message-State: AOJu0Yy5u43NvhIPeFzc/53H2QUL8uH2Ick7AVelKSKH6eZruaxmDqVz nbekteP7ezfEAHCxscqqlg1UkNmVAMoWOnWkQ0lIHXTfq2oVO2Ew X-Google-Smtp-Source: AGHT+IFokcuiNQpmIx+LeDifSxdr+eQv/RRynQlUmI+tAfEfDwliz2LL7xMK+H5ow8Cc9glZnTEo8w== X-Received: by 2002:a17:903:190:b0:1fd:93d2:fba4 with SMTP id d9443c01a7336-1fd93d30202mr37575885ad.48.1721715196030; Mon, 22 Jul 2024 23:13:16 -0700 (PDT) Received: from snowbird ([136.25.84.117]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fd6f44c7b2sm65785955ad.218.2024.07.22.23.13.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jul 2024 23:13:15 -0700 (PDT) Date: Mon, 22 Jul 2024 23:13:10 -0700 From: Dennis Zhou To: Oliver Sang Cc: Boqun Feng , Tejun Heo , Suren Baghdasaryan , oe-lkp@lists.linux.dev, lkp@intel.com, linux-kernel@vger.kernel.org, Andrew Morton , Kent Overstreet , Kees Cook , Alexander Viro , Alex Gaynor , Alice Ryhl , Andreas Hindborg , Benno Lossin , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Christoph Lameter , Gary Guo , Miguel Ojeda , Pasha Tatashin , Peter Zijlstra , Vlastimil Babka , Wedson Almeida Filho , linux-mm@kvack.org, lkmm@lists.linux.dev Subject: Re: [linus:master] [mm] 24e44cc22a: BUG:KCSAN:data-race_in_pcpu_alloc_noprof/pcpu_block_update_hint_alloc Message-ID: References: <202407191651.f24e499d-oliver.sang@intel.com> 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: Hi Oliver, On Tue, Jul 23, 2024 at 02:09:38PM +0800, Oliver Sang wrote: > hi, Dennis Zhou, > > On Mon, Jul 22, 2024 at 10:50:53PM -0700, Dennis Zhou wrote: > > On Mon, Jul 22, 2024 at 01:53:52PM -0700, Boqun Feng wrote: > > > On Mon, Jul 22, 2024 at 11:27:48AM -0700, Dennis Zhou wrote: > > > > Hello, > > > > > > > > On Mon, Jul 22, 2024 at 11:03:00AM -0700, Boqun Feng wrote: > > > > > On Mon, Jul 22, 2024 at 07:52:22AM -1000, Tejun Heo wrote: > > > > > > On Mon, Jul 22, 2024 at 10:47:30AM -0700, Boqun Feng wrote: > > > > > > > This looks like a data race because we read pcpu_nr_empty_pop_pages out > > > > > > > of the lock for a best effort checking, @Tejun, maybe you could confirm > > > > > > > on this? > > > > > > > > > > > > That does sound plausible. > > > > > > > > > > > > > - if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW) > > > > > > > + /* > > > > > > > + * Checks pcpu_nr_empty_pop_pages out of the pcpu_lock, data races may > > > > > > > + * occur but this is just a best-effort checking, everything is synced > > > > > > > + * in pcpu_balance_work. > > > > > > > + */ > > > > > > > + if (data_race(pcpu_nr_empty_pop_pages) < PCPU_EMPTY_POP_PAGES_LOW) > > > > > > > pcpu_schedule_balance_work(); > > > > > > > > > > > > Would it be better to use READ/WRITE_ONCE() for the variable? > > > > > > > > > > > > > > > > For READ/WRITE_ONCE(), we will need to replace all write accesses and > > > > > all out-of-lock read accesses to pcpu_nr_empty_pop_pages, like below. > > > > > It's better in the sense that it doesn't rely on compiler behaviors on > > > > > data races, not sure about the performance impact though. > > > > > > > > > > > > > I think a better alternative is we can move it up into the lock under > > > > area_found. The value gets updated as part of pcpu_alloc_area() as the > > > > code above populates percpu memory that is already allocated. > > > > > > > > > > Not sure I followed what exactly you suggested here because I'm not > > > familiar with the logic, but a simpler version would be: > > > > > > > > > > I believe that's the only naked access of pcpu_nr_empty_pop_pages. So > > I was thinking this'll fix this problem. > > > > I also don't know how to rerun this CI tho.. > > we could test this patch. what's the base? could we apply it directly upon > 24e44cc22a? > > BTW, our bot is not so clever so far to auto test fix patches, so this is kind > of manual effort. due to resource constraint, it will be hard for us to test > each patch (we saw several patches in this thread already) or test very fast. > Ah yeah that makes sense. If you don't mind testing the last one I sent, the one below, that applies cleanly to 24e44cc22a. Thanks, Dennis > > > > --- > > diff --git a/mm/percpu.c b/mm/percpu.c > > index 20d91af8c033..325fb8412e90 100644 > > --- a/mm/percpu.c > > +++ b/mm/percpu.c > > @@ -1864,6 +1864,10 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved, > > > > area_found: > > pcpu_stats_area_alloc(chunk, size); > > + > > + if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW) > > + pcpu_schedule_balance_work(); > > + > > spin_unlock_irqrestore(&pcpu_lock, flags); > > > > /* populate if not all pages are already there */ > > @@ -1891,9 +1895,6 @@ void __percpu *pcpu_alloc_noprof(size_t size, size_t align, bool reserved, > > mutex_unlock(&pcpu_alloc_mutex); > > } > > > > - if (pcpu_nr_empty_pop_pages < PCPU_EMPTY_POP_PAGES_LOW) > > - pcpu_schedule_balance_work(); > > - > > /* clear the areas and return address relative to base address */ > > for_each_possible_cpu(cpu) > > memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);