| Date | Wed, 09 Nov 2011 13:33:40 -0800 | From | Greg KH <> | Subject | [173/264] ext4: fix race in xattr block allocation path |
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3.1-stable review patch. If anyone has any objections, please let me know.
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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;
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