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Date: Fri, 10 Oct 2014 16:23:32 +0200
From: Jan Kara <jack@...e.cz>
To: linux-fsdevel@...r.kernel.org
Cc: linux-ext4@...r.kernel.org, Dave Chinner <david@...morbit.com>,
xfs@....sgi.com, cluster-devel@...hat.com,
Steven Whitehouse <swhiteho@...hat.com>,
Mark Fasheh <mfasheh@...e.com>,
Joel Becker <jlbec@...lplan.org>, ocfs2-devel@....oracle.com,
reiserfs-devel@...r.kernel.org, Jeff Mahoney <jeffm@...e.de>,
Dave Kleikamp <shaggy@...nel.org>,
jfs-discussion@...ts.sourceforge.net, tytso@....edu,
viro@...iv.linux.org.uk, Jan Kara <jack@...e.cz>
Subject: [PATCH] quota: Fix race between dqput() and dquot_scan_active()
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 <jack@...e.cz>
---
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
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