On Fri, Nov 20, 2015 at 06:36:44PM +0900, Hidehiro Kawai wrote:
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 350dfb0..480a4fd 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -445,6 +445,19 @@ extern int sysctl_panic_on_stackoverflow;
>
> extern bool crash_kexec_post_notifiers;
>
> +extern atomic_t panic_cpu;
> +
> +/*
> + * A variant of panic() called from NMI context.
> + * If we've already panicked on this cpu, return from here.
> + */
> +#define nmi_panic(fmt, ...) \
> + do { \
> + int this_cpu = raw_smp_processor_id(); \
> + if (atomic_cmpxchg(&panic_cpu, -1, this_cpu) != this_cpu) \
> + panic(fmt, ##__VA_ARGS__); \
Hmm,
What happens if:
CPU 0: CPU 1:
------ ------
nmi_panic();
nmi_panic();
<external nmi>
nmi_panic();
?
cmpxchg(&panic_cpu, -1, 0) != 0
returns -1 for cpu 0, thus 0 != 0, and sets panic_cpu to 0
cmpxchg(&panic_cpu, -1, 1) != 1
returns 0, and then it too panics, but does not set panic_cpu to 1
Now you have your external NMI triggering on CPU 1
cmpxchg(&panic_cpu, -1, 1) != 1
returns 0 again, and you call panic again within the panic of CPU 1.
Is this OK?
Perhaps you want a per cpu bitmask, and do a test_and_set() on the CPU. That
would prevent any CPU from rerunning a panic() twice on any CPU.
-- Steve
> + } while (0)
> +
> /*
> * Only to be used by arch init code. If the user over-wrote the default
> * CONFIG_PANIC_TIMEOUT, honor it.
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 4579dbb..24ee2ea 100644
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