From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49D4AC43334 for ; Mon, 27 Jun 2022 01:30:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6D39B6B0071; Sun, 26 Jun 2022 21:30:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 682BB8E0002; Sun, 26 Jun 2022 21:30:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 549F98E0001; Sun, 26 Jun 2022 21:30:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 46ADF6B0071 for ; Sun, 26 Jun 2022 21:30:13 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 10F9E2068E for ; Mon, 27 Jun 2022 01:30:13 +0000 (UTC) X-FDA: 79622285106.16.B472B9E Received: from mga04.intel.com (mga04.intel.com [192.55.52.120]) by imf06.hostedemail.com (Postfix) with ESMTP id CC3B018001A for ; Mon, 27 Jun 2022 01:30:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1656293410; x=1687829410; h=from:to:cc:subject:references:date:in-reply-to: message-id:mime-version; bh=NC1jSM8WJJ7D2/nqvABDxS9NRL70yG7/V6OFOiiC/dI=; b=dAQdxeOQq9TTR6ql1E3sgS2obaNNp9SKb50lR6aEc5+SLnTSfjXrT/K/ r7fBIHy6sYFAJnqYhNu+Ge+8EkzUtS+T1C2aYP+QIvxoEol/dNOsNosWA DJwtUfwWsIOr/sVn2p2gKqeNI1xgZdUqwcFSoud4rHJhklS4rInJ6pg72 qkYpNH4YWZCPZcOQRpXH/ItXlRiy4W3g05jXeKp9tzK1wHqH8sqC4jTpx WRHsbclqZ0GZknjMgDOkEZ06qnZRVELm0zKq6YnLp2ZUMULSjuxhw7+Ha PpGeClibwoe0X/qViUQwlZunQboFbZEWyXN2d6kJkpFn0rTVZAIKkH98R A==; X-IronPort-AV: E=McAfee;i="6400,9594,10390"; a="280091198" X-IronPort-AV: E=Sophos;i="5.92,225,1650956400"; d="scan'208";a="280091198" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Jun 2022 18:30:09 -0700 X-IronPort-AV: E=Sophos;i="5.92,225,1650956400"; d="scan'208";a="835973672" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.239.13.94]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Jun 2022 18:30:07 -0700 From: "Huang, Ying" To: Miaohe Lin Cc: , , , , , Subject: Re: [PATCH v3 1/2] mm/swapfile: fix possible data races of inuse_pages References: <20220625093346.48894-1-linmiaohe@huawei.com> <20220625093346.48894-2-linmiaohe@huawei.com> Date: Mon, 27 Jun 2022 09:29:50 +0800 In-Reply-To: <20220625093346.48894-2-linmiaohe@huawei.com> (Miaohe Lin's message of "Sat, 25 Jun 2022 17:33:45 +0800") Message-ID: <874k0699m9.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656293411; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=MGSAo+yN+0ljlW/NhoZu1WsCziInrYjRmlMrYiNy4bM=; b=VQ2Z+x5BGLYtgJapQUqCFeobzSRHCIbQc8JvItdM00xVGYwQneOXV1OWSSrV5ATlLpIV1S x7OFPvkEdYj0Bl2klTfutb2GODTLjMGQ+rldURcqDuBb+22PmewW0Wm4J7jxfuaglsTBBJ XOpPt8mdo4CXGGCOupKrqtHiA/S+Vi4= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=dAQdxeOQ; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf06.hostedemail.com: domain of ying.huang@intel.com has no SPF policy when checking 192.55.52.120) smtp.mailfrom=ying.huang@intel.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656293411; a=rsa-sha256; cv=none; b=YbpvvUtAzlvGD7eynY+dm8vcb0o1OXLSqc7ni9xQRRfnLpXnCguFArup3KlWAfSRx+MQ9Y SERWFQBy/hDnJ/OTarqI2U7D/O5/Pa2SDzFctLAk+kl3QgPG/SeHaAXRVuCv32TP5i9ai3 A+hMXj5n4uTArFciBjJWRkEMFPfPBcc= X-Rspamd-Queue-Id: CC3B018001A Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=dAQdxeOQ; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf06.hostedemail.com: domain of ying.huang@intel.com has no SPF policy when checking 192.55.52.120) smtp.mailfrom=ying.huang@intel.com X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: uadgzkxxccpg17yznrcdhkgsfiwmfytw X-HE-Tag: 1656293410-94978 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Miaohe Lin writes: > si->inuse_pages could still be accessed concurrently now. The plain reads > outside si->lock critical section, i.e. swap_show and si_swapinfo, which > results in data races. READ_ONCE and WRITE_ONCE is used to fix such data > races. Note these data races should be ok because they're just used for > showing swap info. > > Signed-off-by: Miaohe Lin > Reviewed-by: David Hildenbrand Reviewed-by: "Huang, Ying" Thanks! Best Regards, Huang, Ying > --- > mm/swapfile.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/mm/swapfile.c b/mm/swapfile.c > index edc3420d30e7..5c8681a3f1d9 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -695,7 +695,7 @@ static void swap_range_alloc(struct swap_info_struct *si, unsigned long offset, > si->lowest_bit += nr_entries; > if (end == si->highest_bit) > WRITE_ONCE(si->highest_bit, si->highest_bit - nr_entries); > - si->inuse_pages += nr_entries; > + WRITE_ONCE(si->inuse_pages, si->inuse_pages + nr_entries); > if (si->inuse_pages == si->pages) { > si->lowest_bit = si->max; > si->highest_bit = 0; > @@ -732,7 +732,7 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset, > add_to_avail_list(si); > } > atomic_long_add(nr_entries, &nr_swap_pages); > - si->inuse_pages -= nr_entries; > + WRITE_ONCE(si->inuse_pages, si->inuse_pages - nr_entries); > if (si->flags & SWP_BLKDEV) > swap_slot_free_notify = > si->bdev->bd_disk->fops->swap_slot_free_notify; > @@ -2641,7 +2641,7 @@ static int swap_show(struct seq_file *swap, void *v) > } > > bytes = si->pages << (PAGE_SHIFT - 10); > - inuse = si->inuse_pages << (PAGE_SHIFT - 10); > + inuse = READ_ONCE(si->inuse_pages) << (PAGE_SHIFT - 10); > > file = si->swap_file; > len = seq_file_path(swap, file, " \t\n\\"); > @@ -3260,7 +3260,7 @@ void si_swapinfo(struct sysinfo *val) > struct swap_info_struct *si = swap_info[type]; > > if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK)) > - nr_to_be_unused += si->inuse_pages; > + nr_to_be_unused += READ_ONCE(si->inuse_pages); > } > val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused; > val->totalswap = total_swap_pages + nr_to_be_unused;