Re: [PATCH v3 01/22] hardirq/nmi: Allow nested nmi_enter()

Steven Rostedt
2020-02-19T15:31:31Z

On Wed, 19 Feb 2020 15:47:25 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> Since there are already a number of sites (ARM64, PowerPC) that
> effectively nest nmi_enter(), lets make the primitive support this
> before adding even more.
>

> void SMIException(struct pt_regs *regs)
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -71,7 +71,7 @@ extern void irq_exit(void);
> printk_nmi_enter(); \
> lockdep_off(); \
> ftrace_nmi_enter(); \
> - BUG_ON(in_nmi()); \
> + BUG_ON(in_nmi() == NMI_MASK); \
> preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
> rcu_nmi_enter(); \
> trace_hardirq_enter(); \
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -26,13 +26,13 @@
> * PREEMPT_MASK: 0x000000ff
> * SOFTIRQ_MASK: 0x0000ff00
> * HARDIRQ_MASK: 0x000f0000
> - * NMI_MASK: 0x00100000
> + * NMI_MASK: 0x00f00000
> * PREEMPT_NEED_RESCHED: 0x80000000
> */
> #define PREEMPT_BITS 8
> #define SOFTIRQ_BITS 8
> #define HARDIRQ_BITS 4
> -#define NMI_BITS 1
> +#define NMI_BITS 4
>

Probably should document somewhere (in a comment above nmi_enter()?)
that we allow nmi_enter() to nest up to 15 times.

-- Steve