Hi!
On Fri 2020-02-21 08:41:25, Greg Kroah-Hartman wrote:
> From: Changbin Du <changbin.du@xxxxxxxxx>
>
> [ Upstream commit 248ed51048c40d36728e70914e38bffd7821da57 ]
>
> First, printk() is NMI-context safe now since the safe printk() has been
> implemented and it already has an irq_work to make NMI-context safe.
>
> Second, this NMI irq_work actually does not work if a NMI handler causes
> panic by watchdog timeout. It has no chance to run in such case, while
> the safe printk() will flush its per-cpu buffers before panicking.
>
> While at it, repurpose the irq_work callback into a function which
> concentrates the NMI duration checking and makes the code easier to
> follow.
I know there were printk() changes recently, but are they all in 4.19?
Does this actually fix any bug in 4.19?
Best regards,
Pavel
> diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
> index 086cf1d1d71d8..0f8b9b900b0e7 100644
> --- a/arch/x86/kernel/nmi.c
> +++ b/arch/x86/kernel/nmi.c
> @@ -102,18 +102,22 @@ static int __init nmi_warning_debugfs(void)
> }
> fs_initcall(nmi_warning_debugfs);
>
> -static void nmi_max_handler(struct irq_work *w)
> +static void nmi_check_duration(struct nmiaction *action, u64 duration)
> {
> - struct nmiaction *a = container_of(w, struct nmiaction, irq_work);
> + u64 whole_msecs = READ_ONCE(action->max_duration);
> int remainder_ns, decimal_msecs;
> - u64 whole_msecs = READ_ONCE(a->max_duration);
> +
> + if (duration < nmi_longest_ns || duration < action->max_duration)
> + return;
> +
> + action->max_duration = duration;
>
> remainder_ns = do_div(whole_msecs, (1000 * 1000));
> decimal_msecs = remainder_ns / 1000;
>
> printk_ratelimited(KERN_INFO
> "INFO: NMI handler (%ps) took too long to run: %lld.%03d msecs\n",
> - a->handler, whole_msecs, decimal_msecs);
> + action->handler, whole_msecs, decimal_msecs);
> }
>
> static int nmi_handle(unsigned int type, struct pt_regs *regs)
> @@ -140,11 +144,7 @@ static int nmi_handle(unsigned int type, struct pt_regs *regs)
> delta = sched_clock() - delta;
> trace_nmi_handler(a->handler, (int)delta, thishandled);
>
> - if (delta < nmi_longest_ns || delta < a->max_duration)
> - continue;
> -
> - a->max_duration = delta;
> - irq_work_queue(&a->irq_work);
> + nmi_check_duration(a, delta);
> }
>
> rcu_read_unlock();
> @@ -162,8 +162,6 @@ int __register_nmi_handler(unsigned int type, struct nmiaction *action)
> if (!action->handler)
> return -EINVAL;
>
> - init_irq_work(&action->irq_work, nmi_max_handler);
> -
> raw_spin_lock_irqsave(&desc->lock, flags);
>
> /*
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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