On Mon, Jul 30, 2018 at 08:52:07AM -0700, Darrick J. Wong wrote: > /* > * COW fork blocks can overlap data fork blocks even if the blocks > * aren't shared. COW I/O always takes precedent, so we must always > * check for overlap on reflink inodes unless the mapping is already a > * COW one. > * > * It's safe to check the COW fork if_seq here without the ILOCK because > * we've indirectly protected against concurrent updates: writeback has > * the page locked, which prevents concurrent invalidations by reflink > * and directio and prevents concurrent buffered writes to the same > * page. Concurrent changes to other parts of the COW fork will drop > * the i_lock on their way out, which provides the necessary memory > * barrier to ensure that we see the updated if_seq. > */ > > I'm not actually sure about the last sentence anymore -- that's what I > was thinking the first time I looked at this patch, before Dave spoke > up. Yeah, that last sentence looks odd. I'd replace it with: Changes to if_seq always happen under i_lock, which protects against concurrent updates and provides a memory barrier on the way out that ensures that we always see the current value. -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
