On Fri, Jun 08, 2012 at 03:34:46PM -0400, Alain Renaud wrote: > > On filesytems with a block size smaller than PAGE_SIZE we currently have > a problem with unwritten extents. If a we have multi-block page for > which an unwritten extent has been allocated, and only some of the > buffers have been written to, and they are not contiguous, we can expose > stale data from disk in the blocks between the writes after extent > conversion. > > Example of a page with unwritten and real data. > buffer content > 0 empty b_state = 0 > 1 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 2 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 3 empty b_state = 0 > 4 empty b_state = 0 > 5 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 6 DATA b_state = 0x1023 Uptodate,Dirty,Mapped,Unwritten > 7 empty b_state = 0 > > Buffers 1, 2, 5, and 6 have been written to, leaving 0, 3, 4, and 7 empty. > Currently buffers 1, 2, 5, and 6 are added to a single ioend, and when IO has > completed, extent conversion creates a real extent from block 1 through block > 6, leaving 0 and 7 unwritten. However buffers 3 and 4 were not written to > disk, so stale data is exposed from those blocks on a subsequent read. > > Fix this by setting iomap_valid = 0 when we find a buffer that is not > Uptodate. This ensures that buffers 5 and 6 are not added to the same > ioend as buffers 1 and 2. Later these blocks will be converted into two > separate real extents, leaving the blocks in between unwritten. > > Signed-off-by: Alain Renaud <arenaud@xxxxxxx> Looks good to me. It was Dave who had the comments so we'll wait for his second round before pulling this in. I think that cleaning up PageUptodate xfs_convert_page and here in xfs_vm_writepage are valid suggestions, but are better left for a separate patch. Reviewed-by: Ben Myers <bpm@xxxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
