Re: [PATCH V2] xfs: Fix agi&agf ABBA deadlock when performing rename with RENAME_WHITEOUT flag

[Dave Chinner <david@fromorbit.com>]

On Tue, Aug 20, 2019 at 06:51:01AM -0400, Brian Foster wrote:
> On Tue, Aug 20, 2019 at 04:53:22PM +0800, kaixuxia wrote:
> FWIW if we do take that approach, then IMO it's worth reconsidering the
> 1-2 liner I originally proposed to fix the locking. It's slightly hacky,
> but really all three options are hacky in slightly different ways. The
> flipside is it's trivial to implement, review and backport and now would
> be removed shortly thereafter when we replace the on-disk whiteout with
> the in-core fake whiteout thing. Just my .02 though..

We've got to keep the existing whiteout method around for,
essentially, forever, because we have to support kernels that don't
do in-memory translations of DT_WHT to a magic chardev inode and
vice versa (i.e. via mknod). IOWs, we'll need a feature bit to
indicate that we actually have DT_WHT based whiteouts on disk.

So we may as well fix this properly now by restructuring the code as
we will still have to maintain this functionality for a long time to
come.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com