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SubjectRe: [PATCH] NMI watchdog: setup before enabling NMI watchdog

* Aristeu Rozanski <aris@redhat.com> wrote:

> There's a small window when NMI watchdog is being set up that if any NMIs
> are triggered, the NMI code will make make use of not initalized wd_ops
> elements:
> void setup_apic_nmi_watchdog(void *unused)
> {
> if (__get_cpu_var(wd_enabled))
> return;
>
> /* cheap hack to support suspend/resume */
> /* if cpu0 is not active neither should the other cpus */
> if (smp_processor_id() != 0 && atomic_read(&nmi_active) <= 0)
> return;
>
> switch (nmi_watchdog) {
> case NMI_LOCAL_APIC:
> /* enable it before to avoid race with handler */
> --> __get_cpu_var(wd_enabled) = 1;
> --> if (lapic_watchdog_init(nmi_hz) < 0) {
> (...)
> asmlinkage notrace __kprobes void default_do_nmi(struct pt_regs *regs)
> {
> (...)
> if (nmi_watchdog_tick(regs, reason))
> return;
> (...)
> notrace __kprobes int
> nmi_watchdog_tick(struct pt_regs *regs, unsigned reason)
> {
> (...)
> if (!__get_cpu_var(wd_enabled))
> return rc;
> switch (nmi_watchdog) {
> case NMI_LOCAL_APIC:
> rc |= lapic_wd_event(nmi_hz);
> (...)
> int lapic_wd_event(unsigned nmi_hz)
> {
> struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
> u64 ctr;
>
> --> rdmsrl(wd->perfctr_msr, ctr);
>
> and wd->*_msr will be initialized on each processor type specific setup, after
> enabling NMIs for PMIs. Since the counter was just set, the chances of an
> performance counter generated NMI is minimal, but any other unknown NMI would
> trigger the problem. This patch fixes the problem by setting everything up
> before enabling performance counter generated NMIs and will set wd_enabled
> using a callback function.
>
> Signed-off-by: Aristeu Rozanski <aris@redhat.com>
> Acked-by: Don Zickus <dzickus@redhat.com>
> Acked-by: Prarit Bhargava <prarit@redhat.com>
> Acked-by: Vivek Goyal <vgoyal@redhat.com>

applied to tip/x86/nmi-watchdog, thanks Aristeu!

Ingo


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