Currently the fs sync function (super.c:btrfs_sync_fs()) doesn't
wait for delayed work to finish before returning success to the
caller. This change fixes this, ensuring that there's no data loss
if a power failure happens right after fs sync returns success to
the caller and before the next commit happens.
Steps to reproduce the data loss issue:
$ mkfs.btrfs -f /dev/sdb3
$ mount /dev/sdb3 /mnt/btrfs
$ perl -e '$d = ("\x41" x 6001); open($f,">","/mnt/btrfs/foobar"); print $f $d; close($f);' && btrfs fi sync /mnt/btrfs
Right after the btrfs fi sync command (a second or 2 for example), power
off the machine and reboot it. The file will be empty, as it can be verified
after mounting the filesystem and through btrfs-debug-tree:
$ btrfs-debug-tree /dev/sdb3 | egrep '\(257 INODE_ITEM 0\) itemoff' -B 3 -A 8
item 3 key (256 DIR_INDEX 2) itemoff 3751 itemsize 36
location key (257 INODE_ITEM 0) type FILE
namelen 6 datalen 0 name: foobar
item 4 key (257 INODE_ITEM 0) itemoff 3591 itemsize 160
inode generation 7 transid 7 size 0 block group 0 mode 100644 links 1
item 5 key (257 INODE_REF 256) itemoff 3575 itemsize 16
inode ref index 2 namelen 6 name: foobar
checksum tree key (CSUM_TREE ROOT_ITEM 0)
leaf 29429760 items 0 free space 3995 generation 7 owner 7
fs uuid 6192815c-af2a-4b75-b3db-a959ffb6166e
chunk uuid b529c44b-938c-4d3d-910a-013b4700bcae
uuid tree key (UUID_TREE ROOT_ITEM 0)
After this patch, the data loss no longer happens after a power failure and
btrfs-debug-tree shows:
$ btrfs-debug-tree /dev/sdb3 | egrep '\(257 INODE_ITEM 0\) itemoff' -B 3 -A 8
item 3 key (256 DIR_INDEX 2) itemoff 3751 itemsize 36
location key (257 INODE_ITEM 0) type FILE
namelen 6 datalen 0 name: foobar
item 4 key (257 INODE_ITEM 0) itemoff 3591 itemsize 160
inode generation 6 transid 6 size 6001 block group 0 mode 100644 links 1
item 5 key (257 INODE_REF 256) itemoff 3575 itemsize 16
inode ref index 2 namelen 6 name: foobar
item 6 key (257 EXTENT_DATA 0) itemoff 3522 itemsize 53
extent data disk byte 12845056 nr 8192
extent data offset 0 nr 8192 ram 8192
extent compression 0
checksum tree key (CSUM_TREE ROOT_ITEM 0)
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
9b19985986