linux-kernel - clockevents_shutdown vs pending interrupt

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Message-ID: <55892D34.7060504@FreeBSD.org>
Date:	Tue, 23 Jun 2015 12:56:04 +0300
From:	Andriy Gapon <avg@...eBSD.org>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: clockevents_shutdown vs pending interrupt

Pardon if I am asking something obvious or silly...

tick_check_new_device() has the following code:

        if (tick_is_broadcast_device(curdev)) {
                clockevents_shutdown(curdev);
                curdev = NULL;
        }

and

void clockevents_shutdown(struct clock_event_device *dev)
{
        clockevents_set_mode(dev, CLOCK_EVT_MODE_SHUTDOWN);
        dev->next_event.tv64 = KTIME_MAX;
}

This is all done while interrupts are disabled on the current CPU.
But what if there is already a pending interrupt from the current source?
Is it possible that the timer interrupt would be processed by the device that
was put in the shutdown mode?

Some context: I am experiencing exactly the same symptoms as described here
http://thread.gmane.org/gmane.linux.kernel/1483297.  But I run a kernel where
that bug is fixed.  And my problem happens in a VM, so it's possible that there
are timing issues which are very unlikely on real hardware.

-- 
Andriy Gapon
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