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    SubjectRe: Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009
    2009/1/5 john stultz-lkml <johnstul.lkml@gmail.com>:
    > On Fri, Jan 2, 2009 at 4:21 PM, Chris Adams <cmadams@hiwaay.net> wrote:
    >> Basically (to my untrained eye), the leap second code is called from the
    >> timer interrupt handler, which holds xtime_lock. The leap second code
    >> does a printk to notify about the leap second. The printk code tries to
    >> wake up klogd (I assume to prioritize kernel messages), and (under some
    >> conditions), the scheduler attempts to get the current time, which tries
    >> to get xtime_lock => deadlock.
    >
    > This analysis looks correct to me.
    >
    > Grrrr. This has bit us a few times since the "no printk while holding
    > the xtime lock" restriction was added.
    >
    > Thomas: Do you think this warrents adding a check to the printk path
    > to make sure the xtime lock isn't held?

    No.

    > This way we can at least get a
    > warning when someone accidentally adds a printk or calls a function
    > that does while holding the xtime_lock.

    This seems like a basic mistake, that should be avoidable
    with code review. I'm sort-of surprised to even see it; anyone
    even vaguely familiar with that code would spot it quickly.
    Heh. Take that with a grain of salt -- not like I never make
    mistakes ;-/

    I mean, how many more times can the mistake be made?
    I'm arguing its gonna be zero.

    --linas


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