Re: kern/57560: xennetback_xenbus.c rev 1.109 broke guests, causes DOM0 reboot

[Taylor R Campbell <riastradh%NetBSD.org@localhost>]

The following reply was made to PR port-xen/57560; it has been noted by GNATS.

From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
To: Brad Spencer <brad%anduin.eldar.org@localhost>
Cc: gnats-bugs%NetBSD.org@localhost, martin%NetBSD.org@localhost
Subject: Re: kern/57560: xennetback_xenbus.c rev 1.109 broke guests, causes DOM0 reboot
Date: Fri, 4 Aug 2023 20:19:33 +0000

 I reverted the commits on HEAD and pulled the revert up to netbsd-10,
 so the immediate problem should be addressed.
 
 However, the code is also slightly problematic because it's still
 missing a barrier in one place, and still using a much-too-expensive
 barrier (even on x86!) in the loop in another place, and still has
 several nonsensical barriers in other places that can't hurt
 correctness but do hurt understandability and maintainability.
 
 So I went through to try to redo the changes more carefully.  If you
 have the opportunity to test or bisect on another patch, I've drafted
 a series of changes, attached:
 
 - The .diff file is a single diff of the whole changes.  If it works,
   great -- I can commit.  But if not:
 
 - The .patch file is a series of individual changes for bisection to
   see exactly which one breaks it.