Re: [PATCH] hrtimer, add expiry time overflow check in hrtimer_interrupt

[John Stultz]

On 04/08/2013 07:53 AM, Rik van Riel wrote:
> On 04/08/2013 08:47 AM, Prarit Bhargava wrote:
>
> > When we change the system time to a low value like this, the value of
> > timekeeper->offs_real will be a negative value.
> >
> > It seems that the WARN occurs because an hrtimer has been started in 
> > the time
> > between the releasing of the timekeeper lock and the IPI call (via a 
> > call to
> > on_each_cpu) in clock_was_set() in the do_settimeofday() code. The 
> > end result
> > is that a REALTIME_CLOCK timer has been added with softexpires = 
> > expires =
> > KTIME_MAX.  The hrtimer_interrupt() fires/is called and the loop at
> > kernel/hrtimer.c:1289 is executed.  In this loop the code subtracts the
> > clock base's offset (which was set to timekeeper->offs_real in
> > do_settimeofday()) from the current hrtimer_cpu_base->expiry value 
> > (which
> > was KTIME_MAX):
> >
> >     KTIME_MAX - (a negative value) = overflow
> >
> > A simple check for an overflow can resolve this problem.  Using 
> > KTIME_MAX
> > instead of the overflow value will result in the hrtimer function 
> > being run,
> > and the reprogramming of the timer after that.
> >
> > Signed-off-by: Prarit Bhargava <prarit@xxxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: John Stultz <john.stultz@xxxxxxxxxx>
>
> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

Queued in my fortglx/3.10/time branch.

thanks
-john


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