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SubjectRe: [PATCH printk v3 4/6] printk: remove NMI tracking
On Thu 2021-06-24 13:17:46, John Ogness wrote:
> All NMI contexts are handled the same as the safe context: store the
> message and defer printing. There is no need to have special NMI
> context tracking for this. Using in_nmi() is enough.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> Reviewed-by: Petr Mladek <pmladek@suse.com>
> ---
> arch/arm/kernel/smp.c | 2 --
> arch/powerpc/kexec/crash.c | 3 ---
> include/linux/hardirq.h | 2 --
> include/linux/printk.h | 12 ------------
> init/Kconfig | 5 -----
> kernel/printk/internal.h | 6 ------
> kernel/printk/printk_safe.c | 37 +------------------------------------
> kernel/trace/trace.c | 2 --
> 8 files changed, 1 insertion(+), 68 deletions(-)
>
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 74679240a9d8..0dd2d733ad62 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -668,9 +668,7 @@ static void do_handle_IPI(int ipinr)
> break;
>
> case IPI_CPU_BACKTRACE:
> - printk_nmi_enter();
> nmi_cpu_backtrace(get_irq_regs());
> - printk_nmi_exit();

It looks to me that in_nmi() returns false here. As a result,
nmi_cpu_backtrace() might newly call consoles immediately.

If I recall correctly, arm does not have a proper NMI.
And this is just some special case of a "normal" IRQ.

And indeed, nmi_enter() is called only from handle_fiq_as_nmi()
and it is just a boiler plate.

If I am right, we should replace printk_nmi_enter() with
printk_safe_enter_irqsave(flags) or so.

Even better solution might be to call this within
nmi_enter()/nmi_exit(). But I am not sure if this is what
the arm people want.

Best Regards,
Petr

PS: Sigh, I have skipped this patch yesterday because it already had
my Reviewed-by. And I missed it before...

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