[PATCH 3.2 071/164] ext4: move check under lock scope to close a race.

[Ben Hutchings]

3.2.70-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Davide Italiano <dccitaliano@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
[bwh: Backported to 3.2:
 - Adjust context
 - Add the 'out' label]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/ext4/extents.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4470,13 +4470,6 @@ long ext4_fallocate(struct file *file, i
 	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, i
 	 */
 	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);

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