[PATCH 3.16 81/99] ext4: fix a potential fiemap/page fault deadlock w/ inline_data

From: Ben Hutchings
Date: Tue Apr 02 2019 - 09:45:11 EST

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


From: Theodore Ts'o <tytso@xxxxxxx>

commit 2b08b1f12cd664dc7d5c84ead9ff25ae97ad5491 upstream.

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

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@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
fs/ext4/inline.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -1846,12 +1846,12 @@ int ext4_inline_data_fiemap(struct 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);
+ if (physical)
+ error = fiemap_fill_next_extent(fieinfo, start, physical,
+ inline_len, flags);
return (error < 0 ? error : 0);