Re: [PATCH 2/4] nmi: add generic nmi tracking state

Andrew Morton
2009-02-06T07:18:34Z

On Fri, 06 Feb 2009 01:53:54 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <srostedt@redhat.com>
>
> This code adds an in_nmi() macro that uses the current tasks preempt count
> to track when it is in NMI context. Other parts of the kernel can
> use this to determine if the context is in NMI context or not.
>
> This code was inspired by the -rt patch in_nmi version that was
> written by Peter Zijlstra.
>
> Reported-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
> include/linux/hardirq.h | 15 +++++++++++++++
> 1 files changed, 15 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
> index f832883..f3cf86e 100644
> --- a/include/linux/hardirq.h
> +++ b/include/linux/hardirq.h
> @@ -61,6 +61,12 @@
> #error PREEMPT_ACTIVE is too low!
> #endif
>
> +#define NMI_OFFSET (PREEMPT_ACTIVE << 1)
> +
> +#if NMI_OFFSET >= 0x80000000
> +#error PREEMPT_ACTIVE too high!
> +#endif
> +
> #define hardirq_count() (preempt_count() & HARDIRQ_MASK)
> #define softirq_count() (preempt_count() & SOFTIRQ_MASK)
> #define irq_count() (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK))
> @@ -73,6 +79,11 @@
> #define in_softirq() (softirq_count())
> #define in_interrupt() (irq_count())
>
> +/*
> + * Are we in NMI context?
> + */
> +#define in_nmi() (preempt_count() & NMI_OFFSET)
> +
> #if defined(CONFIG_PREEMPT)
> # define PREEMPT_INATOMIC_BASE kernel_locked()
> # define PREEMPT_CHECK_OFFSET 1
> @@ -167,6 +178,8 @@ extern void irq_exit(void);
> #define nmi_enter() \
> do { \
> ftrace_nmi_enter(); \
> + BUG_ON(in_nmi()); \
> + add_preempt_count(NMI_OFFSET); \
> lockdep_off(); \
> rcu_nmi_enter(); \
> __irq_enter(); \
> @@ -177,6 +190,8 @@ extern void irq_exit(void);
> __irq_exit(); \
> rcu_nmi_exit(); \
> lockdep_on(); \
> + BUG_ON(!in_nmi()); \
> + sub_preempt_count(NMI_OFFSET); \
> ftrace_nmi_exit(); \
> } while (0)
>

Well that was tidy.

We're sure that no present or future architecture will for some weird
reason nest NMIs?