On Mon, Mar 12, 2018 at 11:21:56PM +0800, Eryu Guan wrote: > Currently in ext4 direct write path, we update i_disksize only when > new eof is greater than i_size, and don't update it even when new > eof is greater than i_disksize but less than i_size. This doesn't > work well with delalloc buffer write, which updates i_size and > i_disksize only when delalloc blocks are resolved (at writeback > time), the i_disksize from direct write can be lost if a previous > buffer write succeeded at write time but failed at writeback time, > then results in corrupted ondisk inode size. > > Consider this case, first buffer write 4k data to a new file at > offset 16k with delayed allocation, then direct write 4k data to the > same file at offset 4k before delalloc blocks are resolved, which > doesn't update i_disksize because it writes within i_size(20k), but > the extent tree metadata has been committed in journal. Then > writeback of the delalloc blocks fails (due to device error etc.), > and i_size/i_disksize from buffer write can't be written to disk > (still zero). A subsequent umount/mount cycle recovers journal and > writes extent tree metadata from direct write to disk, but with > i_disksize being zero. > > Fix it by updating i_disksize too in direct write path when new eof > is greater than i_disksize but less than i_size, so i_disksize is > always consistent with direct write. > > This fixes occasional i_size corruption in fstests generic/475. > > Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx> Updated, thanks. - Ted
