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authorJan Kara <jack@suse.cz>2014-02-20 17:02:27 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-03-06 21:30:12 -0800
commit4480120a6cf3c834cc73431d615bb716be586f2f (patch)
tree2295f596dcce1c61a092008eba09a9d034019122 /fs
parent3e66969eabfa905623cd6677c08e523a6b9410da (diff)
downloadlinaro-lsk-4480120a6cf3c834cc73431d615bb716be586f2f.tar.gz
quota: Fix race between dqput() and dquot_scan_active()
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@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/quota/dquot.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 3e64169ef52..38802d68396 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 */