From patchwork Tue Jul 2 16:38:39 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Durrant X-Patchwork-Id: 11028283 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D83DC138B for ; Tue, 2 Jul 2019 16:40:41 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C50B9284F5 for ; Tue, 2 Jul 2019 16:40:41 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B97252858E; Tue, 2 Jul 2019 16:40:41 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 516FB284F5 for ; Tue, 2 Jul 2019 16:40:41 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1hiLnt-0001ig-IH; Tue, 02 Jul 2019 16:38:49 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.89) (envelope-from ) id 1hiLnr-0001iH-UO for xen-devel@lists.xenproject.org; Tue, 02 Jul 2019 16:38:47 +0000 X-Inumbo-ID: dc2bda94-9ce7-11e9-83a6-5349a050a6a1 Received: from esa2.hc3370-68.iphmx.com (unknown [216.71.145.153]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id dc2bda94-9ce7-11e9-83a6-5349a050a6a1; Tue, 02 Jul 2019 16:38:46 +0000 (UTC) Authentication-Results: esa2.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none; spf=None smtp.pra=paul.durrant@citrix.com; spf=Pass smtp.mailfrom=Paul.Durrant@citrix.com; spf=None smtp.helo=postmaster@mail.citrix.com Received-SPF: None (esa2.hc3370-68.iphmx.com: no sender authenticity information available from domain of paul.durrant@citrix.com) identity=pra; client-ip=162.221.158.21; receiver=esa2.hc3370-68.iphmx.com; envelope-from="Paul.Durrant@citrix.com"; x-sender="paul.durrant@citrix.com"; x-conformance=sidf_compatible Received-SPF: Pass (esa2.hc3370-68.iphmx.com: domain of Paul.Durrant@citrix.com designates 162.221.158.21 as permitted sender) identity=mailfrom; client-ip=162.221.158.21; receiver=esa2.hc3370-68.iphmx.com; envelope-from="Paul.Durrant@citrix.com"; x-sender="Paul.Durrant@citrix.com"; x-conformance=sidf_compatible; x-record-type="v=spf1"; x-record-text="v=spf1 ip4:209.167.231.154 ip4:178.63.86.133 ip4:195.66.111.40/30 ip4:85.115.9.32/28 ip4:199.102.83.4 ip4:192.28.146.160 ip4:192.28.146.107 ip4:216.52.6.88 ip4:216.52.6.188 ip4:162.221.158.21 ip4:162.221.156.83 ~all" Received-SPF: None (esa2.hc3370-68.iphmx.com: no sender authenticity information available from domain of postmaster@mail.citrix.com) identity=helo; client-ip=162.221.158.21; receiver=esa2.hc3370-68.iphmx.com; envelope-from="Paul.Durrant@citrix.com"; x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible IronPort-SDR: 1HVVlpBeEyqFY8ue3C4/YfjNRVbEb+HZuPKDv/1luvh/ZkjLiWOFyH5ggji4vddcvDj0msDkW3 7/QbVmFO/gyX6b/o/QkytEcYlSztTizZ4hZHsEC7JY9/cFVNNPhiJ+K9zuJKXL8E2HceVYefgY 9JQu06DMojCgLWNNOVYwfwNnkLa0nrFGWEuztZD50UWoQ+EvmZ9rWFa83pD4kLP7WHRFDYFB7v 2spnYLX9nUL6dmRhP/5a9hcVWrrFWZI/X+RbqZSl6fpISdhgv2SH/9WV1Ph1sj3/QhhorMPN4y NIU= X-SBRS: 2.7 X-MesageID: 2501599 X-Ironport-Server: esa2.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.63,443,1557201600"; d="scan'208";a="2501599" From: Paul Durrant To: Date: Tue, 2 Jul 2019 17:38:39 +0100 Message-ID: <20190702163840.2107-3-paul.durrant@citrix.com> X-Mailer: git-send-email 2.20.1.2.gb21ebb671 In-Reply-To: <20190702163840.2107-1-paul.durrant@citrix.com> References: <20190702163840.2107-1-paul.durrant@citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH 2/3] xmalloc: don't evaluate ADD_REGION without holding the pool lock X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Stefano Stabellini , Wei Liu , Konrad Rzeszutek Wilk , George Dunlap , Andrew Cooper , Ian Jackson , Tim Deegan , Julien Grall , Paul Durrant , Jan Beulich Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP It's not safe to add a region without holding the lock, but this is exactly what may happen if two threads race entering xmem_pool_alloc() before the init_region is set. This patch instead checks for init_region under lock, drops the lock if it needs to allocate a page, takes the lock, adds the region and then confirms init_region is still unset before pointing it at the newly added region. Thus, it is possible that a race may cause an extra region to be added, but there will be no pool metadata corruption. Signed-off-by: Paul Durrant --- Cc: Andrew Cooper Cc: George Dunlap Cc: Ian Jackson Cc: Jan Beulich Cc: Julien Grall Cc: Konrad Rzeszutek Wilk Cc: Stefano Stabellini Cc: Tim Deegan Cc: Wei Liu --- xen/common/xmalloc_tlsf.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/xen/common/xmalloc_tlsf.c b/xen/common/xmalloc_tlsf.c index 6d889b7bdc..71597c3590 100644 --- a/xen/common/xmalloc_tlsf.c +++ b/xen/common/xmalloc_tlsf.c @@ -380,18 +380,22 @@ void *xmem_pool_alloc(unsigned long size, struct xmem_pool *pool) int fl, sl; unsigned long tmp_size; + spin_lock(&pool->lock); if ( pool->init_region == NULL ) { + spin_unlock(&pool->lock); if ( (region = pool->get_mem(pool->init_size)) == NULL ) goto out; + spin_lock(&pool->lock); ADD_REGION(region, pool->init_size, pool); - pool->init_region = region; + /* Re-check since the lock was dropped */ + if ( pool->init_region == NULL ) + pool->init_region = region; } size = (size < MIN_BLOCK_SIZE) ? MIN_BLOCK_SIZE : ROUNDUP_SIZE(size); /* Rounding up the requested size and calculating fl and sl */ - spin_lock(&pool->lock); retry_find: MAPPING_SEARCH(&size, &fl, &sl);