From patchwork Wed Mar 5 14:36:51 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 327022 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 1C5822C0091 for ; Thu, 6 Mar 2014 01:40:35 +1100 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1WLCzm-0005zF-I1; Wed, 05 Mar 2014 14:40:30 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1WLCxe-0004tY-Sd for kernel-team@lists.ubuntu.com; Wed, 05 Mar 2014 14:38:18 +0000 Received: from bl6-122-102.dsl.telepac.pt ([82.155.122.102] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1WLCxe-0002VF-Kh; Wed, 05 Mar 2014 14:38:18 +0000 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Subject: [PATCH 3.5 47/62] quota: Fix race between dqput() and dquot_scan_active() Date: Wed, 5 Mar 2014 14:36:51 +0000 Message-Id: <1394030226-26652-48-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.9.0 In-Reply-To: <1394030226-26652-1-git-send-email-luis.henriques@canonical.com> References: <1394030226-26652-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.5 Cc: Jan Kara X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com 3.5.7.32 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Jan Kara commit 1362f4ea20fa63688ba6026e586d9746ff13a846 upstream. Currently last dqput() can race with dquot_scan_active() causing it to call callback for an already deactivated dquot. The race is as follows: CPU1 CPU2 dqput() spin_lock(&dq_list_lock); if (atomic_read(&dquot->dq_count) > 1) { - not taken if (test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) { spin_unlock(&dq_list_lock); ->release_dquot(dquot); if (atomic_read(&dquot->dq_count) > 1) - not taken dquot_scan_active() spin_lock(&dq_list_lock); if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) - not taken atomic_inc(&dquot->dq_count); spin_unlock(&dq_list_lock); - proceeds to release dquot ret = fn(dquot, priv); - called for inactive dquot Fix the problem by making sure possible ->release_dquot() is finished by the time we call the callback and new calls to it will notice reference dquot_scan_active() has taken and bail out. Signed-off-by: Jan Kara Signed-off-by: Luis Henriques --- fs/quota/dquot.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index 10cbe84..000831b 100644 --- a/fs/quota/dquot.c +++ b/fs/quota/dquot.c @@ -580,9 +580,17 @@ int dquot_scan_active(struct super_block *sb, dqstats_inc(DQST_LOOKUPS); dqput(old_dquot); old_dquot = dquot; - ret = fn(dquot, priv); - if (ret < 0) - goto out; + /* + * ->release_dquot() can be racing with us. Our reference + * protects us from new calls to it so just wait for any + * outstanding call and recheck the DQ_ACTIVE_B after that. + */ + wait_on_dquot(dquot); + if (test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) { + ret = fn(dquot, priv); + if (ret < 0) + goto out; + } spin_lock(&dq_list_lock); /* We are safe to continue now because our dquot could not * be moved out of the inuse list while we hold the reference */