On Wed, Sep 05, 2018 at 09:33:34PM -0400, Steven Rostedt wrote:
> do_idle {
>
> [interrupts enabled]
>
> <interrupt> [interrupts disabled]
> TRACE_IRQS_OFF [lockdep says irqs off]
> [...]
> TRACE_IRQS_IRET
> test if pt_regs say return to interrupts enabled [yes]
> TRACE_IRQS_ON [lockdep says irqs are on]
>
> <nmi>
> nmi_enter() {
> printk_nmi_enter() [traced by ftrace]
> [ hit ftrace breakpoint ]
> <breakpoint exception>
> TRACE_IRQS_OFF [lockdep says irqs off]
> [...]
> TRACE_IRQS_IRET [return from breakpoint]
> test if pt_regs say interrupts enabled [no]
> [iret back to interrupt]
> [iret back to code]
>
> tick_nohz_idle_enter() {
>
> lockdep_assert_irqs_enabled() [lockdep say no!]
Isn't the problem that we muck with the IRQ state from NMI context? We
shouldn't be doing that.
The thing is, since we trace the IRQ state from within IRQ-disable,
since that's the only IRQ-safe option, it is very much not NMI-safe.
Your patch might avoid the symptom, but I don't think it cures the
fundamental problem.
