This is a note to let you know that I've just added the patch titled
quota: Fix race between dqput() and dquot_scan_active()
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
quota-fix-race-between-dqput-and-dquot_scan_active.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1362f4ea20fa63688ba6026e586d9746ff13a846 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 20 Feb 2014 17:02:27 +0100
Subject: quota: Fix race between dqput() and dquot_scan_active()
From: Jan Kara <jack@xxxxxxx>
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 <jack@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/quota/dquot.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -580,9 +580,17 @@ int dquot_scan_active(struct super_block
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 */
Patches currently in stable-queue which might be from jack@xxxxxxx are
queue-3.4/quota-fix-race-between-dqput-and-dquot_scan_active.patch
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