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    SubjectRe: [PATCH] clocksource, prevent overflow in clocksource_cyc2ns
    On Wed, 18 Apr 2012, John Stultz wrote:
    > On 04/18/2012 04:59 PM, Prarit Bhargava wrote:
    > >
    > > Hey John,
    > >
    > > Thanks for continuing to work on this. Coincidentally that exact patch was
    > > my
    > > first attempt at resolving the problem as well. The problem is that even
    > > after
    > > touching the clocksource watchdog and restoring irqs the printk buffer can
    > > take
    > > a LONG time to flush -- and that still will cause an overflow comparison.
    > > So
    > > fixing it with just a touch_clocksource_watchdog() isn't the right thing to
    > > do
    > > IMO. Maybe a combination of the printk() patch you suggested earlier and
    > > the
    > > touch_clocksource_watchdog() is the right way to go but I'll leave that up
    > > to
    > > tglx and yourself to decide on a correct fix.
    > :( That's a bummer. Something similar may be useful on the printk side as
    > well.

    No. The show_state() part prints into the buffer. But it's not
    guaranteed that the buffer is flushed right away. It could be flushed
    later as well in a different context. And of course the flush code
    runs with interrupts disabled and dumping out a gazillion of lines
    over serial will cause the same hickup. Just planting random
    touch_watchdog() calls into the code is not the right approach,

    We should think about the reasons why we have interrupts disabled for
    so much time. Is that really, really necessary ?



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