On Thu 21-01-16 10:46:01, Ross Zwisler wrote: > Previously in dax_writeback_one() we cleared the PAGECACHE_TAG_TOWRITE flag > before we had actually flushed the tagged radix tree entry to media. This > is incorrect because of the following race: > > Thread 1 Thread 2 > -------- -------- > dax_writeback_mapping_range() > tag entry with PAGECACHE_TAG_TOWRITE > dax_writeback_mapping_range() > tag entry with PAGECACHE_TAG_TOWRITE > dax_writeback_one() > radix_tree_tag_clear(TOWRITE) > TOWRITE flag is no longer set, > find_get_entries_tag() finds no > entries, return > flush entry to media > > In this case thread 1 returns before the data for the dirty entry is > actually durable on media. > > Fix this by only clearing the PAGECACHE_TAG_TOWRITE flag after all flushing > is complete. > > Signed-off-by: Ross Zwisler <[email protected]> > Reported-by: Jan Kara <[email protected]>
Looks good. You can add: Reviewed-by: Jan Kara <[email protected]> Honza > --- > fs/dax.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index cee9e1b..d589113 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -407,8 +407,6 @@ static int dax_writeback_one(struct block_device *bdev, > if (!radix_tree_tag_get(page_tree, index, PAGECACHE_TAG_TOWRITE)) > goto unlock; > > - radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE); > - > if (WARN_ON_ONCE(type != RADIX_DAX_PTE && type != RADIX_DAX_PMD)) { > ret = -EIO; > goto unlock; > @@ -432,6 +430,10 @@ static int dax_writeback_one(struct block_device *bdev, > } > > wb_cache_pmem(dax.addr, dax.size); > + > + spin_lock_irq(&mapping->tree_lock); > + radix_tree_tag_clear(page_tree, index, PAGECACHE_TAG_TOWRITE); > + spin_unlock_irq(&mapping->tree_lock); > unmap: > dax_unmap_atomic(bdev, &dax); > return ret; > -- > 2.5.0 > > -- Jan Kara <[email protected]> SUSE Labs, CR
