path: root/fs
diff options
authorEric Sandeen <sandeen@redhat.com>2011-10-29 10:15:35 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2011-11-11 09:43:54 -0800
commit87556ecf5d093a7d083ce909476783bf98dc4725 (patch)
tree647cc8db0131b6f1b0d4911aef07c821963273d0 /fs
parent6ff60a6de3b107b9c78eb10b2c9a9987bab5138c (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')
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index c757adc9725..19fe4e3d39e 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;