quota: fix dquot_disable vs dquot_transfer race v2

I've got following lockup:
dquot_disable                              dquot_transfer
                                            ->dqget()
					       sb_has_quota_active
dqopt->flags &= ~dquot_state_flag(f, cnt)      atomic_inc(dq->dq_count)
 ->drop_dquot_ref(sb, cnt);
    down_write(dqptr_sem)
    inode->i_dquot[cnt] = NULL              ->__dquot_transfer
invalidate_dquots(sb, cnt);		       down_write(&dqptr_sem)
  ->wait for dq_wait_unused		       inode->i_dquot = new_dquot
  /* wait forever */                            ^^^^New quota user^^^^^^

We cannot allow new references to dquots from inodes after drop_dquot_ref()
has removed them.  We have to recheck quota state under dqptr_sem and before
assignment, as we do it in dquot_initialize().

Signed-off-by: Dmitry Monakhov <dmonakhov@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 12 insertions, 6 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index aad1316a977f..ed14beea8fe3 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -1736,6 +1736,7 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
         qsize_t rsv_space = 0;
         struct dquot *transfer_from[MAXQUOTAS] = {};
         int cnt, ret = 0;
+        char is_valid[MAXQUOTAS] = {};
         char warntype_to[MAXQUOTAS];
         char warntype_from_inodes[MAXQUOTAS], warntype_from_space[MAXQUOTAS];
 
@@ -1757,8 +1758,15 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
         space = cur_space + rsv_space;
         /* Build the transfer_from list and check the limits */
         for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
+                /*
+                 * Skip changes for same uid or gid or for turned off quota-type.
+                 */
                 if (!transfer_to[cnt])
                         continue;
+                /* Avoid races with quotaoff() */
+                if (!sb_has_quota_active(inode->i_sb, cnt))
+                        continue;
+                is_valid[cnt] = 1;
                 transfer_from[cnt] = inode->i_dquot[cnt];
                 ret = check_idq(transfer_to[cnt], 1, warntype_to + cnt);
                 if (ret)
@@ -1772,12 +1780,8 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
          * Finally perform the needed transfer from transfer_from to transfer_to
          */
         for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
-                /*
-                 * Skip changes for same uid or gid or for turned off quota-type.
-                 */
-                if (!transfer_to[cnt])
+                if (!is_valid[cnt])
                         continue;
-
                 /* Due to IO error we might not have transfer_from[] structure */
                 if (transfer_from[cnt]) {
                         warntype_from_inodes[cnt] =
@@ -1803,7 +1807,9 @@ int __dquot_transfer(struct inode *inode, struct dquot **transfer_to)
         mark_all_dquot_dirty(transfer_to);
         /* Pass back references to put */
         for (cnt = 0; cnt < MAXQUOTAS; cnt++)
-                transfer_to[cnt] = transfer_from[cnt];
+                if (is_valid[cnt])
+                        transfer_to[cnt] = transfer_from[cnt];
+
 warn:
         flush_warnings(transfer_to, warntype_to);
         flush_warnings(transfer_from, warntype_from_inodes);