Commit 248ed510 authored by Changbin Du's avatar Changbin Du Committed by Borislav Petkov
Browse files

x86/nmi: Remove irq_work from the long duration NMI handler 



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.

 [ bp: Massage. ]

Signed-off-by: default avatarChangbin Du <changbin.du@gmail.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200111125427.15662-1-changbin.du@gmail.com
parent 36209766

arch/x86/include/asm/nmi.h

+0 −1
Original line number Diff line number Diff line
@@ -41,7 +41,6 @@ struct nmiaction { 
	struct list_head	list;

	nmi_handler_t		handler;

	u64			max_duration;

	struct irq_work		irq_work;

	unsigned long		flags;

	const char		*name;

};

arch/x86/kernel/nmi.c

+9 −11
Original line number Diff line number Diff line
@@ -104,18 +104,22 @@ 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)
@@ -142,11 +146,7 @@ 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();
@@ -164,8 +164,6 @@ 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);



	/*

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