| From 6d6a435190bdf2e04c9465cde5bdc3ac68cf11a4 Mon Sep 17 00:00:00 2001 |
| From: Eric Sandeen <sandeen@redhat.com> |
| Date: Sat, 29 Oct 2011 10:15:35 -0400 |
| Subject: ext4: fix race in xattr block allocation path |
| |
| From: Eric Sandeen <sandeen@redhat.com> |
| |
| commit 6d6a435190bdf2e04c9465cde5bdc3ac68cf11a4 upstream. |
| |
| Ceph users reported that when using Ceph on ext4, the filesystem |
| would often become corrupted, containing inodes with incorrect |
| i_blocks counters. |
| |
| I managed to reproduce this with a very hacked-up "streamtest" |
| binary from the Ceph tree. |
| |
| Ceph is doing a lot of xattr writes, to out-of-inode blocks. |
| There is also another thread which does sync_file_range and close, |
| of the same files. The problem appears to happen due to this race: |
| |
| sync/flush thread xattr-set thread |
| ----------------- ---------------- |
| |
| do_writepages ext4_xattr_set |
| ext4_da_writepages ext4_xattr_set_handle |
| mpage_da_map_blocks ext4_xattr_block_set |
| set DELALLOC_RESERVE |
| ext4_new_meta_blocks |
| ext4_mb_new_blocks |
| if (!i_delalloc_reserved_flag) |
| vfs_dq_alloc_block |
| ext4_get_blocks |
| down_write(i_data_sem) |
| set i_delalloc_reserved_flag |
| ... |
| up_write(i_data_sem) |
| if (i_delalloc_reserved_flag) |
| vfs_dq_alloc_block_nofail |
| |
| |
| In other words, the sync/flush thread pops in and sets |
| i_delalloc_reserved_flag on the inode, which makes the xattr thread |
| think that it's in a delalloc path in ext4_new_meta_blocks(), |
| and add the block for a second time, after already having added |
| it once in the !i_delalloc_reserved_flag case in ext4_mb_new_blocks |
| |
| The real problem is that we shouldn't be using the DELALLOC_RESERVED |
| state flag, and instead we should be passing |
| EXT4_GET_BLOCKS_DELALLOC_RESERVE down to ext4_map_blocks() instead of |
| using an inode state flag. We'll fix this for now with using |
| i_data_sem to prevent this race, but this is really not the right way |
| to fix things. |
| |
| Signed-off-by: Eric Sandeen <sandeen@redhat.com> |
| Signed-off-by: "Theodore Ts'o" <tytso@mit.edu> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| fs/ext4/xattr.c | 6 ++++++ |
| 1 file changed, 6 insertions(+) |
| |
| --- a/fs/ext4/xattr.c |
| +++ b/fs/ext4/xattr.c |
| @@ -820,8 +820,14 @@ inserted: |
| if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) |
| goal = goal & EXT4_MAX_BLOCK_FILE_PHYS; |
| |
| + /* |
| + * take i_data_sem because we will test |
| + * i_delalloc_reserved_flag in ext4_mb_new_blocks |
| + */ |
| + down_read((&EXT4_I(inode)->i_data_sem)); |
| block = ext4_new_meta_blocks(handle, inode, goal, 0, |
| NULL, &error); |
| + up_read((&EXT4_I(inode)->i_data_sem)); |
| if (error) |
| goto cleanup; |
| |