From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f176.google.com (mail-pl1-f176.google.com [209.85.214.176]) (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 1ED0828370; Tue, 23 Jul 2024 05:50:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.176 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721713859; cv=none; b=ITWOHuqtaQB5Yvf2gxkcpQ8/YZeoN0MMLAOrIplfvNsD6rKaqQ27Z/Nq+JKkuu9UiYU9mmsk79maFMrQfGM9bSAoPccHaa6lp8oIz0GllBqMjdZu1QfPmOWWnmpkarmSNGBVr2XP3jKOlFTXLG0YZeyCrOdSa+tBAqprZ7N4iNg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1721713859; c=relaxed/simple; bh=6tYYKQYNkRScY15H5x6zL1HtxOURu19MpuubO+4vKM0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=F2VD4VR4Cu1QUN4Vi23/vohmj2CZgh2knWGabN2rRpn+JXShgVCwBqLHD+DSvWytg4rUgkRq8LDzlqRsfT6HnbSCxP1s/Z0z/lSoUK9XaausdB2TzGaubo6WDtf3MiambXR2bDiY0vOBuA/JxBkWFHYuIG1Q1Q8AB8vxownVVzc= 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=209.85.214.176 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-f176.google.com with SMTP id d9443c01a7336-1fc6a017abdso23320955ad.0; Mon, 22 Jul 2024 22:50:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1721713857; x=1722318657; 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=HAi76Fbb14aLD72KSDP4ZLSN99eyDyIsZtCeNe0d2u8=; b=q1el4l/AB4bhwIZhvyeazCUB12QqREp7KBtjEiAbYUuHgGy1IfCC6xwOEwz5CraM3+ oJUamq6EzN85JocsBFcBmJJ5Ibv7oVP6SmjAKELawL50m7I2hDIJbr3S3yFkr2DH08JY nn04xipdyRkJwA6TdeN8devXj4qsswRuHLM7KxYhqFKKewZaf06v8+SVZfbbf8xxJCIM GrEWSLIVMjiwYYuimTNTF5P3Uf+qKZHsK0HIiSeZqHuIh90c4TlKBWGn+QE05pv01tym 29OUidffI5DNHxQtN030CHL2ptDObyCWyX/I0hGCF1ycFk8P0gluiarEohkkBXgG+2ZS o2/A== X-Forwarded-Encrypted: i=1; AJvYcCWTKMIVN4vF7frp9byPC7MAY3MtsCG7R7C6PErvlVkekpnuWuw/U92yr5N+PfncRl2UK24TeDQqNJr+NneGNBuErQEenvMwYgPoSOWJ7pwXU9YcDlw1BfPT1ZACkg== X-Gm-Message-State: AOJu0YxZC4tmmiDIXbgWUSwpfJeJJXpMtoIIXl5NtN4inYDYHUiQ7VrU APg0XoES9psqX1Ej52S7RhTsVTPdTY2KT81Q+NB4+dIIV/fEZKSC X-Google-Smtp-Source: AGHT+IGI5WT7ey25jg4G2dYdrX/Y37jBH63oL83DdgNLhILixfslqS9am3ee4OUjXlB4bSi2bGXT2Q== X-Received: by 2002:a17:903:2448:b0:1fd:6677:69b4 with SMTP id d9443c01a7336-1fd74660a7dmr64169625ad.49.1721713857175; Mon, 22 Jul 2024 22:50:57 -0700 (PDT) Received: from snowbird ([136.25.84.117]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-1fd6f48ca81sm65316435ad.299.2024.07.22.22.50.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jul 2024 22:50:56 -0700 (PDT) Date: Mon, 22 Jul 2024 22:50:53 -0700 From: Dennis Zhou To: Boqun Feng Cc: Tejun Heo , kernel test robot , 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: lkmm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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.. --- 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);