From: Jan Kara Subject: [PATCH] quota: Fix race between dqput() and dquot_scan_active() Date: Fri, 10 Oct 2014 16:23:32 +0200 Message-ID: <1412951028-4085-28-git-send-email-jack@suse.cz> References: <1412951028-4085-1-git-send-email-jack@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Dave Kleikamp , jfs-discussion@lists.sourceforge.net, tytso@mit.edu, Jeff Mahoney , Mark Fasheh , Dave Chinner , reiserfs-devel@vger.kernel.org, xfs@oss.sgi.com, cluster-devel@redhat.com, Joel Becker , Jan Kara , linux-ext4@vger.kernel.org, Steven Whitehouse , ocfs2-devel@oss.oracle.com, viro@zeniv.linux.org.uk To: linux-fsdevel@vger.kernel.org Return-path: In-Reply-To: <1412951028-4085-1-git-send-email-jack@suse.cz> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: jfs-discussion-bounces@lists.sourceforge.net List-Id: linux-ext4.vger.kernel.org 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 --- fs/quota/dquot.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) This is the last patch needed to make ocfs2 quotas rock solid in my testing. I will carry it in my tree and push it to Linus soon. diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index 831d49a4111f..cfc8dcc16043 100644 --- a/fs/quota/dquot.c +++ b/fs/quota/dquot.c @@ -581,9 +581,17 @@ 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 */ -- 1.8.1.4 ------------------------------------------------------------------------------ Meet PCI DSS 3.0 Compliance Requirements with EventLog Analyzer Achieve PCI DSS 3.0 Compliant Status with Out-of-the-box PCI DSS Reports Are you Audit-Ready for PCI DSS 3.0 Compliance? Download White paper Comply to PCI DSS 3.0 Requirement 10 and 11.5 with EventLog Analyzer http://pubads.g.doubleclick.net/gampad/clk?id=154622311&iu=/4140/ostg.clktrk