Re: [Xen-devel] [PATCH] BUG() on soft lockup upon suspend/resume

[Glauber de Oliveira Costa <gcosta@xxxxxxxxxx>]

> 
> > In systems with vcpu > 1, a BUG due to a detected soft lockup seems to be
> > triggered after system resume/suspend. This is probably due to the lack of
> > seqlocking around the region that does the local time processing.
> 
> We do SMP save/restore tests regularly and do not see this issue. It ought
> to be avoided by the fact that, when we bring up a CPU, we
> touch_softlockup_watchdog() in cpu_bringup(), before enabling interrupts.
> For CPU0 on resume, the touch is done in time_resume() in
> arch/i386/kernel/time-xen.c.

This happens not only (once) when the system comes back. It do happen a
lot after it. So even if the first touch is right, I suspect this issue
is more related to a situation in which we are already resumed for a
long time, with all set up
> 
> I think we need to understand the issue you are hitting a bit more before
> deciding on the right fix.

Right, here it goes more info:

I'm on a 8-way x86_64 machine, and This is the sort of info I see
repeatedly:

BUG: soft lockup detected on CPU#1!

Call Trace:
 <IRQ>  [<ffffffff802ace9d>] softlockup_tick+0xf8/0x113
 [<ffffffff8026d591>] timer_interrupt+0x38a/0x3d8
 [<ffffffff80210e87>] handle_IRQ_event+0x2d/0x60
 [<ffffffff802ad1e6>] __do_IRQ+0xa5/0x107
 [<ffffffff8028be7a>] _local_bh_enable+0x61/0xc5
 [<ffffffff8026b4c9>] do_IRQ+0xe7/0xf5
 [<ffffffff8039386e>] evtchn_do_upcall+0x86/0xe0
 [<ffffffff8025e2a2>] do_hypervisor_callback+0x1e/0x2c
 <EOI>  [<ffffffff802063aa>] hypercall_page+0x3aa/0x1000
 [<ffffffff802063aa>] hypercall_page+0x3aa/0x1000
 [<ffffffff8026cb13>] raw_safe_halt+0x84/0xa8
 [<ffffffff8026a121>] xen_idle+0x38/0x4a
 [<ffffffff80248e66>] cpu_idle+0x97/0xba

It obviously never happen on CPU#0, but I see it on all others (vcpus=4)

If you have any other opinion on what else may be causing this, it's
very welcome. I'll keep investigating.


-- 
Glauber de Oliveira Costa
Red Hat Inc.
"Free as in Freedom"

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