[Pkg-xen-devel] Bug#991967: Simply ACPI powerdown/reset issue?

[Elliott Mitchell]

On Tue, Sep 21, 2021 at 06:33:20AM -0400, Chuck Zmudzinski wrote:
> I presume you are suggesting I try booting 4.19.181-1 on the
> current version of Xen-4.14 for bullseye as a dom0. I am not
> inclined to try it until an official Debian developer endorses
> your opinion that the bug I am seeing is distinct
> from #991967, at which point I will report the bug I am
> seeing as a new bug.

Chuck Zmudzinski you are getting rather close to my threshold for calling
harrassment.  You're not /quite/ there, but I'm concerned.


Since the purpose of the bug reports is to find and diagnose bugs, I did
a bit of experimentation and made some observations.

I checked out the Debian Xen source via git.  I got the current
"master" branch which is presently the candidate 4.14.3-1 version,
which includes urgent fixes.  The hash is:
e7a17db0305c8de891b366ad37777528e5a43015

On top of this I cherry-picked 3 commits from Xen's main branch:
5a4087004d1adbbb223925f3306db0e5824a2bdc
0f089bbf43ecce6f27576cb548ba4341d0ec46a8
bc141e8ca56200bdd0a12e04a6ebff3c19d6c27b

(these can be retrieved via Xen's gitweb at
https://xenbits.xen.org/gitweb/?p=xen.git;a=patch;h=<$hash> which is
suitable for the `git am` command)

With these I built 4.14.3-1 and then tried kernels 4.19.181-1 and
4.19.194-3 (this system is presently mostly on oldstable).  The results
were:

Xen 4.14.3-1 with Linux 4.19.181-1: system reboots were successful

Xen 4.14.3-1 with Linux 4.19.194-3: system reboots hung

Unfortunately I was too quick at installing the rebuilt 4.14.3-1 and I
missed trying the vanilla Debian 4.14.2+25-gb6a8c4f72d-2 with
Linux 4.19.181-1.  I believe this combination would have hung during
reboot.


As such, I believe there are in fact two distinct bugs being observed.
The presence of EITHER of these is sufficient to cause hangs during
powerdown or reboot.

First, some patch originally from Linux's main branch breaks Xen reboots
was backported somewhere between 4.19.181-1 and 4.19.194-3.  This may
either have been introduced before 5.10 diverged from main, or may also
have been backported to 5.10.  THIS is Debian bug #991967.

Second, the Xen patch 3c428e9ecb1f290689080c11e0c37b793425bef1 which is
valuable to ARM devices breaks reboots and powerdowns on x86.  This is
correctly fixed by 0f089bbf43ecce6f27576cb548ba4341d0ec46a8.  Presently
this has no Debian bug report.


The first is presently unidentified, someone enthusiastic either needs to
read git logs/source code, or bisect and build to find where it got
broken.

The second we seem to have a fix.  The only question is how many patches
to cherry pick?  bc141e8ca562 is non-urgent as it is merely superficial
and not needed for functionality.
5a4087004d1a is a workaround for Linux kernel breakage, but how likely
are we to see that fixed in the Linux kernel packages?  The fix is
well-contained and needed for some highly popular ARM devices.


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