On Wed, Aug 29, 2018 at 08:36:25AM +1000, Dave Chinner wrote:
> On Mon, Aug 27, 2018 at 10:25:47AM -0400, Brian Foster wrote:
> > xfs_trans_brelse() is a bit of a historical mess, similar to
> > xfs_buf_item_unlock(). It is unnecessarily verbose, has snippets of
> > commented out code, inconsistency with regard to stale items, etc.
> >
> > Clean up xfs_trans_brelse() to use similar logic and flow as
> > xfs_buf_item_unlock() with regard to bli reference count handling.
> > This patch makes no functional changes, but facilitates further
> > refactoring of the common bli reference count handling code.
> >
> > Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
>
> Nice! I like it a lot. Couple of minor things....
>
> > - ASSERT(!(bip->bli_flags & XFS_BLI_LOGGED));
> > -
> > /*
> > - * Free up the log item descriptor tracking the released item.
> > + * Unlink the log item from the transaction and clear the hold flag, if
> > + * set. We wouldn't want the next user of the buffer to get confused.
> > */
> > + ASSERT(!(bip->bli_flags & XFS_BLI_LOGGED));
> > xfs_trans_del_item(&bip->bli_item);
> > -
> > - /*
> > - * Clear the hold flag in the buf log item if it is set.
> > - * We wouldn't want the next user of the buffer to
> > - * get confused.
> > - */
> > - if (bip->bli_flags & XFS_BLI_HOLD) {
> > + if (bip->bli_flags & XFS_BLI_HOLD)
> > bip->bli_flags &= ~XFS_BLI_HOLD;
> > - }
>
> May as well just unconditionally clear XFS_BLI_HOLD - the cache line
> is already dirty by this point, so it's less code than checking to
> see if we do need to clear it.
>
Good point.
> > /*
> > - * Drop our reference to the buf log item.
> > + * Drop the reference to the bli. At this point, the bli must be either
> > + * freed or dirty (or both). If freed, there are a couple cases where we
> > + * are responsible to free the item. If the bli is clean, we're the last
> > + * user of it. If the fs has shut down, the bli may be dirty and AIL
> > + * resident, but won't ever be written back.
> so we may also need to
> * remove it from the AIL before freeing it
> > */
Tweaked... though note that this comment ends up split/reworked in the
subsequent patch.
Brian
> > freed = atomic_dec_and_test(&bip->bli_refcount);
> > -
> > - /*
> > - * If the buf item is not tracking data in the log, then we must free it
> > - * before releasing the buffer back to the free pool.
> > - *
> > - * If the fs has shutdown and we dropped the last reference, it may fall
> > - * on us to release a (possibly dirty) bli if it never made it to the
> > - * AIL (e.g., the aborted unpin already happened and didn't release it
> > - * due to our reference). Since we're already shutdown and need
> > - * ail_lock, just force remove from the AIL and release the bli here.
> > - */
> > - if (XFS_FORCED_SHUTDOWN(tp->t_mountp) && freed) {
> > - xfs_trans_ail_remove(&bip->bli_item, SHUTDOWN_LOG_IO_ERROR);
> > - xfs_buf_item_relse(bp);
> > - } else if (!(bip->bli_flags & XFS_BLI_DIRTY)) {
> > -/***
> > - ASSERT(bp->b_pincount == 0);
> > -***/
> > - ASSERT(atomic_read(&bip->bli_refcount) == 0);
> > - ASSERT(!test_bit(XFS_LI_IN_AIL, &bip->bli_item.li_flags));
> > - ASSERT(!(bip->bli_flags & XFS_BLI_INODE_ALLOC_BUF));
> > - xfs_buf_item_relse(bp);
> > + dirty = bip->bli_flags & XFS_BLI_DIRTY;
> > + ASSERT(freed || dirty);
> > + if (freed) {
> > + bool abort = XFS_FORCED_SHUTDOWN(tp->t_mountp);
> > + ASSERT(abort || !test_bit(XFS_LI_IN_AIL, &bip->bli_item.li_flags));
> > + if (abort)
> > + xfs_trans_ail_remove(&bip->bli_item, SHUTDOWN_LOG_IO_ERROR);
> > + if (!dirty || abort)
> > + xfs_buf_item_relse(bp);
> > }
>
> That, overall, is much nicer than the current code and worth doing,
> I think.
>
> Cheers,
>
> Dave.
>
> --
> Dave Chinner
> david@xxxxxxxxxxxxx
