quota: Fix possible races during quota loading
When loading new quota structure from disk, there is a possibility caller
of dqget() will see uninitialized data due to CPU reordering loads or
stores - loads from dquot can be reordered before test of DQ_ACTIVE_B
bit or setting of this bit could be reordered before filling of the
structure. Fix the issue by adding proper memory barriers.
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 7e0137b..e8467dc 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -411,6 +411,8 @@
ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot);
if (ret < 0)
goto out_iolock;
+ /* Make sure flags update is visible after dquot has been filled */
+ smp_mb__before_atomic();
set_bit(DQ_READ_B, &dquot->dq_flags);
/* Instantiate dquot if needed */
if (!test_bit(DQ_ACTIVE_B, &dquot->dq_flags) && !dquot->dq_off) {
@@ -427,6 +429,11 @@
goto out_iolock;
}
}
+ /*
+ * Make sure flags update is visible after on-disk struct has been
+ * allocated. Paired with smp_rmb() in dqget().
+ */
+ smp_mb__before_atomic();
set_bit(DQ_ACTIVE_B, &dquot->dq_flags);
out_iolock:
mutex_unlock(&dqopt->dqio_mutex);
@@ -887,6 +894,11 @@
goto out;
}
}
+ /*
+ * Make sure following reads see filled structure - paired with
+ * smp_mb__before_atomic() in dquot_acquire().
+ */
+ smp_rmb();
#ifdef CONFIG_QUOTA_DEBUG
BUG_ON(!dquot->dq_sb); /* Has somebody invalidated entry under us? */
#endif