Miao pointed out there's a problem with mixing dio writes and buffered reads. If the read happens between us invalidating the page range and actually locking the extent we can bring in pages into page cache. Then once the write finishes if somebody tries to read again it will just find uptodate pages and we'll read stale data. So we need to lock the extent and check for uptodate bits in the range. If there are uptodate bits we need to unlock and invalidate again. This will keep this race from happening since we will hold the extent locked until we create the ordered extent, and then teh read side always waits for ordered extents. Thanks,
Signed-off-by: Josef Bacik <jo...@redhat.com> --- fs/btrfs/inode.c | 26 +++++++++++++++++++++++--- 1 files changed, 23 insertions(+), 3 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 9d8c45d..9b631eb 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -6360,12 +6360,32 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb, */ ordered = btrfs_lookup_ordered_range(inode, lockstart, lockend - lockstart + 1); - if (!ordered) + + /* + * We need to make sure there are no buffered pages in this + * range either, we could have raced between the invalidate in + * generic_file_direct_write and locking the extent. The + * invalidate needs to happen so that reads after a write do not + * get stale data. + */ + if (!ordered && (!writing || + !test_range_bit(&BTRFS_I(inode)->io_tree, + lockstart, lockend, EXTENT_UPTODATE, 0, + cached_state))) break; + unlock_extent_cached(&BTRFS_I(inode)->io_tree, lockstart, lockend, &cached_state, GFP_NOFS); - btrfs_start_ordered_extent(inode, ordered, 1); - btrfs_put_ordered_extent(ordered); + + if (ordered) { + btrfs_start_ordered_extent(inode, ordered, 1); + btrfs_put_ordered_extent(ordered); + } else { + invalidate_mapping_pages(file->f_mapping, + lockstart >> PAGE_CACHE_SHIFT, + lockend >> PAGE_CACHE_SHIFT); + } + cond_resched(); } -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html