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    SubjectRe: [PATCH] hangcheck-timer is broken on x86
    On Fri, 26 Mar 2010 14:24:23 -0700
    Andrew Morton <akpm@linux-foundation.org> wrote:

    > On Tue, 23 Mar 2010 23:36:11 -0400
    > Yury Polyanskiy <ypolyans@princeton.edu> wrote:
    >
    > > The drivers/char/hangcheck-timer.c is doubly broken. First, the
    > > following line overflows unsigned long:
    > > # define TIMER_FREQ (HZ*loops_per_jiffy)
    > >
    > > Second, and more importantly, loops_per_jiffy has little to do with the conversion from the
    > > the time scale of get_cycles() (aka rdtsc) to the time scale of jiffies.
    >
    > It's a bit odd to have a driver be this broken on x86_32 for five years
    > without anyone noticing. What are the user-visible effects of these
    > shortcomings?

    When the overflown value of TIMER_FREQ is abnormally low, it spams the
    syslog with KERN_CRIT messages "Hangcheck: hangcheck value past margin!"
    But whether it happens or not depends on HZ and lpj in a complex way.
    People have hit it occasionally as far as google search can tell.

    >
    > Also, please do send us a Signed-off-by: for this patch, as explained
    > in Documentation/SubmittingPatches, thanks.
    >

    Sorry.

    Signed-off-by: Yury Polyanskiy <polyanskiy@gmail.com>

    Thank you Andrew!

    Yury
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