ext4: fix a potential fiemap/page fault deadlock w/ inline_data

The ext4_inline_data_fiemap() function calls fiemap_fill_next_extent()
while still holding the xattr semaphore.  This is not necessary and it
triggers a circular lockdep warning.  This is because
fiemap_fill_next_extent() could trigger a page fault when it writes
into page which triggers a page fault.  If that page is mmaped from
the inline file in question, this could very well result in a
deadlock.

This problem can be reproduced using generic/519 with a file system
configuration which has the inline_data feature enabled.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 27373d88b5f0115341b4c574599bd21ee8767fee..56f6e1782d5f7db9148e0b868e0297362aa7bb24 100644 (file)
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1890,12 +1890,12 @@ int ext4_inline_data_fiemap(struct inode *inode,
        physical += (char *)ext4_raw_inode(&iloc) - iloc.bh->b_data;
        physical += offsetof(struct ext4_inode, i_block);
 
-       if (physical)
-               error = fiemap_fill_next_extent(fieinfo, start, physical,
-                                               inline_len, flags);
        brelse(iloc.bh);
 out:
        up_read(&EXT4_I(inode)->xattr_sem);
+       if (physical)
+               error = fiemap_fill_next_extent(fieinfo, start, physical,
+                                               inline_len, flags);
        return (error < 0 ? error : 0);
 }