Hi Derek,
I wish to gladly inform you that I've fixed the bug preventing suspend with
Tboot.
It was in the piece of code that you've highlighted - the atomic increment on
ap_wfs_count variable need have been moved into the else clause of the
following if statement, something like this:
static int tboot_dying_cpu(unsigned int cpu) {
if (num_online_cpus() == 1) {
if (tboot_wait_for_aps(atomic_read(&ap_wfs_count)))
return -EBUSY;
} else
atomic_inc(&ap_wfs_count);
return 0;
}
Otherwise, when the procedure shutdown all APs, BSP was also counted in as one
of them, thus creating a mismatch between what kernel had counted and what
TBOOT reported back to it.
This caused a kernel panic, which froze the machine while putting it into
suspend.
I've sent a version of TBOOT Live Image equipped with this patch of the kernel
to our validation teams and I'm awaiting their response after the weekend.
If I get positive results from their tests I will try and have this patch
attached to the official kernel repository and featured in versions 5.19 and up.
Kind regards,
Paweł
-----Original Message-----
From: Randzio, Pawel
Sent: Friday, May 13, 2022 12:12 PM
To: 'Derek Dolney' <z...@posteo.net>; Łukasz Hawryłko <luk...@hawrylko.pl>
Cc: tboot-devel@lists.sourceforge.net
Subject: RE: [tboot-devel] suspend problem since kernel 5.15
Hi Derek,
I've also been picking at that issue for the past few months and reached the
same wall as you have with the -EBUSY callback return, although your message
kind of gives me a new idea for where to look for the root cause as it seems I
have not tracked all possible callbacks.
I'm not a kernel developer either and honestly debugging that S3 issue is
troublesome to me too, to say the least. If anyone on this mailing list has any
idea how to further the debugging or even better - solve this issue, please
feel free to share ideas.
On a side note, please add Vincent into the communication, that might speed up
the process.
Vincent may add others that could know what might be going on with that issue.
Thanks,
Paweł
-----Original Message-----
From: Derek Dolney <z...@posteo.net>
Sent: Thursday, May 12, 2022 6:20 PM
To: Łukasz Hawryłko <luk...@hawrylko.pl>; tboot-devel@lists.sourceforge.net
Subject: Re: [tboot-devel] suspend problem since kernel 5.15
I have been working on this as best I can. However, I confess that I am not a
kernel developer and have really no understanding of these tboot internals.
Nevertheless here is a brief update. Please anyone feel free to share any ideas
how to move forward to some resolution.
I got a desktop machine with rs232 serial output running tboot and reproduced
the suspend problem that way and with this setup I can collect kernel printk
and also cpu hotplug (cpuhp) tracing output. I have also thankfully got quite a
bit of help from Vincent Donnefort who wrote the cpuhp changes (the commit I
posted) that have exposed the issue. He has been very helpful, let me try to
tell you what we have figured out.
On suspend, I get into the tboot callback:
static int tboot_dying_cpu(unsigned int cpu) {
atomic_inc(&ap_wfs_count);
if (num_online_cpus() == 1) {
if (tboot_wait_for_aps(atomic_read(&ap_wfs_count)))
return -EBUSY;
}
return 0;
}
but the tboot_wait_for_aps times out for me so the callback returns EBUSY. The
problem with that happening is that there is not a rollback mechanism in place
at this point in the cpuhp sequence. So I mean from cpuhp point of view, there
is not even a mechanism to handle the tboot callback failure. Besides that, we
don't know what could be a sensible thing to do in the case of EBUSY. What does
it mean tboot is busy and what should be done about it? Please help us to
understand.
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