On Thu 19-03-09 00:12:22, Aneesh Kumar K.V wrote: > On Tue, Mar 17, 2009 at 06:33:54PM +0100, Jan Kara wrote: > > Assume the following situation: > > Filesystem with blocksize < pagesize - suppose blocksize = 1024, > > pagesize = 4096. File 'f' has first four blocks already allocated. > > (line with "state:" contains the state of buffers in the page - m = mapped, > > u = uptodate, d = dirty) > > > > process 1: process 2: > > > > write to 'f' bytes 0 - 1024 > > state: |mud,-,-,-|, page dirty > > write to 'f' bytes 1024 - 4096: > > __block_prepare_write() maps blocks > > state: |mud,m,m,m|, page dirty > > we fail to copy data -> copied = 0 > > block_write_end() does nothing > > page gets unlocked > > > If copied = 0 then in block_write_end we do > > page_zero_new_buffers(page, start+copied, start+len > > which would mean we should not see garbage. But this will zero only *new* buffers - so if they are already allocated, get_block() won't set new flag and they won't be zeroed... But I'm not saying I understand why this seems to help against a corruption under UML because we don't seem to be writing !uptodate buffers there. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
