quota: Fix dquot_transfer for filesystems different from ext4

Commit fd8fbfc1 modified the way we find amount of reserved space
belonging to an inode. The amount of reserved space is checked
from dquot_transfer and thus inode_reserved_space gets called
even for filesystems that don't provide get_reserved_space callback
which results in a BUG.

Fix the problem by checking get_reserved_space callback and return 0 if
the filesystem does not provide it.

CC: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index dea86abdf2e7..3fc62b097bed 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -1377,6 +1377,9 @@ static void inode_sub_rsv_space(struct inode *inode, qsize_t number)
 static qsize_t inode_get_rsv_space(struct inode *inode)
 {
         qsize_t ret;
+
+        if (!inode->i_sb->dq_op->get_reserved_space)
+                return 0;
         spin_lock(&inode->i_lock);
         ret = *inode_reserved_space(inode);
         spin_unlock(&inode->i_lock);