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

From: John Stultz
Date: Mon Apr 08 2013 - 15:51:14 EST

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

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.


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