| Message ID | 4EA5E702.8030303@redhat.com |
|---|---|
| State | Accepted, archived |
| Headers | show |
On Mon, Oct 24, 2011 at 05:30:26PM -0500, Eric Sandeen wrote: > Ceph users reported that when using Ceph on ext4, the filesystem > would often become corrupted, containing inodes with incorrect > i_blocks counters. > > ... > > 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 > > I think this can be as simple as taking i_data_sem before we > go down the new metablock path, so that we won't be testing > i_delalloc_reserved_flag in a race with xt4_get_blocks setting it. > > Signed-off-by: Eric Sandeen <sandeen@redhat.com> Thanks, applied for now. > > This seems like slight abuse of i_data_sem though, since we are > not modifying i_data[] in the inode on the xattr path. But nothing > else protects readers of i_delalloc_reserved_flag in other > threads. Thoughts? Agreed, we really should be depending on the EXT4_GET_BLOCK_DELALLOC_RESERVE and EXT4_MB_DELALLOC_RESERVED flags. I can't remember what caused us to plumb in the i_state flag, but that's clearly a hack which is biting us hard. I'll take this patch for now since it fixes a real problem, but we should figure out a better way of fixing this, hopefully that results in the i_state flag going away. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index e4d0fca..dcebdbd 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -819,8 +819,14 @@ 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, NULL, &error); + up_read((&EXT4_I(inode)->i_data_sem)); if (error) goto cleanup;
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 I think this can be as simple as taking i_data_sem before we go down the new metablock path, so that we won't be testing i_delalloc_reserved_flag in a race with xt4_get_blocks setting it. Signed-off-by: Eric Sandeen <sandeen@redhat.com> --- This seems like slight abuse of i_data_sem though, since we are not modifying i_data[] in the inode on the xattr path. But nothing else protects readers of i_delalloc_reserved_flag in other threads. Thoughts? p.s. this almost feels like it needs quite a rework, I'm trying to remember why we set a "we are in a delalloc path" in an inode flag rather than as something passed through the callchain arguments, but I'm fuzzy on these twisty paths. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html