diff options
| author | Eric Sandeen <sandeen@redhat.com> | 2011-10-29 10:15:35 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-11-11 09:43:54 -0800 |
| commit | 87556ecf5d093a7d083ce909476783bf98dc4725 (patch) | |
| tree | 647cc8db0131b6f1b0d4911aef07c821963273d0 /fs | |
| parent | 6ff60a6de3b107b9c78eb10b2c9a9987bab5138c (diff) | |
ext4: fix race in xattr block allocation path
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>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/ext4/xattr.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index c757adc97250..19fe4e3d39ec 100644 --- 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; |