Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU

Don Zickus
2010-10-19T18:37:40Z

On Tue, Oct 19, 2010 at 06:25:07PM +0200, Robert Richter wrote:
> On 19.10.10 17:07:01, Robert Richter wrote:
> > On 15.10.10 22:22:17, Don Zickus wrote:
> > > From: Huang Ying <ying.huang@intel.com>
> > >
> > > In original NMI handler, NMI reason io port (0x61) is only processed
> > > on BSP. This makes it impossible to hot-remove BSP. To solve the
> > > issue, a raw spinlock is used to make the port can be processed on any
> > > CPU.
> > >
> > > Signed-off-by: Huang Ying <ying.huang@intel.com>
> > > Signed-off-by: Don Zickus <dzickus@redhat.com>
> > > ---
> > > arch/x86/kernel/traps.c | 45 +++++++++++++++++++++++++--------------------
> > > 1 files changed, 25 insertions(+), 20 deletions(-)
>
> > > @@ -400,28 +405,28 @@ static notrace __kprobes void default_do_nmi(struct pt_regs *regs)
> > > return;
> > >
> > > /* Non-CPU-specific NMI: NMI sources can be processed on any CPU */
> > > - cpu = smp_processor_id();
> > > - /* Only the BSP gets external NMIs from the system. */
> > > - if (!cpu) {
> > > - reason = get_nmi_reason();
> > > - if (reason & NMI_REASON_MASK) {
> > > - if (notify_die(DIE_NMI, "nmi", regs, reason, 2, SIGINT)
> > > - == NOTIFY_STOP)
> > > - return;
> > > - if (reason & NMI_REASON_SERR)
> > > - pci_serr_error(reason, regs);
> > > - else if (reason & NMI_REASON_IOCHK)
> > > - io_check_error(reason, regs);
> > > + raw_spin_lock(&nmi_reason_lock);
> >
> > What about using raw_spin_trylock() instead? We don't have to wait
> > here since we are already processing it by another cpu.
>
> This would avoid a global lock and also deadlocking in case of a
> potential #gp in the nmi handler.

I would feel more comfortable with it too. I can't find a reason where
trylock would do harm.

Cheers,
Don