On Wed, Nov 14, 2018 at 09:19:26AM -0500, Brian Foster wrote: > On Wed, Nov 07, 2018 at 05:31:25PM +1100, Dave Chinner wrote: > > From: Dave Chinner <dchinner@xxxxxxxxxx> > > > > For data integrity purposes, we need to write back the entire > > filesystem block when asked to sync a sub-block range of the file. > > When the filesystem block size is larger than the page size, this > > means we need to convert single page integrity writes into whole > > block integrity writes. We do this by extending the writepage range > > to filesystem block granularity and alignment. > > > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > > --- > > fs/xfs/xfs_aops.c | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > > index f6ef9e0a7312..5334f16be166 100644 > > --- a/fs/xfs/xfs_aops.c > > +++ b/fs/xfs/xfs_aops.c > > @@ -900,6 +900,7 @@ xfs_vm_writepages( > > .io_type = XFS_IO_HOLE, > > }; > > int ret; > > + unsigned bsize = i_blocksize(mapping->host); > > > > /* > > * Refuse to write pages out if we are called from reclaim context. > > @@ -922,6 +923,19 @@ xfs_vm_writepages( > > if (WARN_ON_ONCE(current->flags & PF_MEMALLOC_NOFS)) > > return 0; > > > > + /* > > + * If the block size is larger than page size, extent the incoming write > > + * request to fsb granularity and alignment. This is a requirement for > > + * data integrity operations and it doesn't hurt for other write > > + * operations, so do it unconditionally. > > + */ > > + if (wbc->range_start) > > + wbc->range_start = round_down(wbc->range_start, bsize); > > + if (wbc->range_end != LLONG_MAX) > > + wbc->range_end = round_up(wbc->range_end, bsize); > > + if (wbc->nr_to_write < wbc->range_end - wbc->range_start) > > + wbc->nr_to_write = round_up(wbc->nr_to_write, bsize); > > + > > This latter bit causes endless writeback loops in tests such as > generic/475 (I think I reproduced it with xfs/141 as well). The Yup, I've seen that, but haven't fixed it yet because I still haven't climbed out of the dedupe/clone/copy file range data corruption hole that fsx pulled the lid of. Basically, I can't get back to working on bs > ps until I get the stuff we actually support working correctly first... > writeback infrastructure samples ->nr_to_write before and after > ->writepages() calls to identify progress. Unconditionally bumping it to > something larger than the original value can lead to an underflow in the > writeback code that seems to throw things off. E.g., see the following > wb tracepoints (w/ 4k block and page size): > > kworker/u8:13-189 [003] ...1 317.968147: writeback_single_inode_start: bdi 253:9: ino=8389005 state=I_DIRTY_PAGES|I_SYNC dirtied_when=4294773087 age=211 index=0 to_write=1024 wrote=0 cgroup_ino=4294967295 > kworker/u8:13-189 [003] ...1 317.968150: writeback_single_inode: bdi 253:9: ino=8389005 state=I_DIRTY_PAGES|I_SYNC dirtied_when=4294773087 age=211 index=0 to_write=1024 wrote=18446744073709548544 cgroup_ino=4294967295 > > The wrote value goes from 0 to garbage and writeback_sb_inodes() uses > the same basic calculation for 'wrote.' Easy enough to fix, just stash the originals and restore them once done. > > BTW, I haven't gone through the broader set, but just looking at this > bit what's the purpose of rounding ->nr_to_write (which is a page count) > to a block size in the first place? fsync on a single page range. We write that page, allocate the block (which spans 16 pages), and then return from writeback leaving 15/16 pages on that block still dirty in memory. Then we force the log, pushing the allocation and metadata to disk. Crash. On recovery, we expose 15/16 pages of stale data because we only wrote one of the pages over the block during fsync. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
