Re: [PATCH RESEND] x86/smpboot: Unbreak CPU0 hotplug

[Ingo Molnar]

* Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:

> Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> writes:
> 
> > A hang on CPU0 onlining after a preceding offlining is observed. Trace
> > shows that CPU0 is stuck in check_tsc_sync_target() waiting for source
> > CPU to run check_tsc_sync_source() but this never happens. Source CPU,
> > in its turn, is stuck on synchronize_sched() which is called from
> > native_cpu_up() -> do_boot_cpu() -> unregister_nmi_handler().
> >
> > Fix the issue by moving unregister_nmi_handler() from do_boot_cpu() to
> > native_cpu_up() after cpu onlining is done.

Looks like a classic ABBA deadlock, due to the use of synchronize_sched() in 
unregister_nmi_handler(), right?

> >
> > Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> > ---
> > It's been awile since my v1 submission, no comments so far. Resending.
> 
> Sorry, but 
> 
> ping?
> 
> I haven't received a single comment on this since the initial submission
> on June, 26 - is it so bad? :-)

So the fix looks good to me at first sight, but wanted to wait for Thomas to ack 
it - once he gets back from vacation.

Thanks,

	Ingo