ext4: move check under lock scope to close a race.

commit 280227a75b56ab5d35854f3a77ef74a7ad56a203 upstream.

fallocate() checks that the file is extent-based and returns
EOPNOTSUPP in case is not. Other tasks can convert from and to
indirect and extent so it's safe to check only after grabbing
the inode mutex.

Signed-off-by: Davide Italiano <dccitaliano@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.2:
 - Adjust context
 - Add the 'out' label]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 834d9a1..0eed964 100644 (file)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4470,13 +4470,6 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
        struct ext4_map_blocks map;
        unsigned int credits, blkbits = inode->i_blkbits;
 
-       /*
-        * currently supporting (pre)allocate mode for extent-based
-        * files _only_
-        */
-       if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS)))
-               return -EOPNOTSUPP;
-
        /* Return error if mode is not supported */
        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;
@@ -4497,6 +4490,15 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
         */
        credits = ext4_chunk_trans_blocks(inode, max_blocks);
        mutex_lock(&inode->i_mutex);
+
+       /*
+        * We only support preallocation for extent-based files only
+        */
+       if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
+               ret = -EOPNOTSUPP;
+               goto out;
+       }
+
        ret = inode_newsize_ok(inode, (len + offset));
        if (ret) {
                mutex_unlock(&inode->i_mutex);
@@ -4553,6 +4555,7 @@ retry:
                ret = 0;
                goto retry;
        }
+out:
        mutex_unlock(&inode->i_mutex);
        trace_ext4_fallocate_exit(inode, offset, max_blocks,
                                ret > 0 ? ret2 : ret);