Re: [patch 1/2] posix-cpu-timers: Unbreak timer rearming
- Date: Fri, 11 Jan 2019 08:10:33 -0800
- From: "H.J. Lu" <hjl.tools@xxxxxxxxx>
- Subject: Re: [patch 1/2] posix-cpu-timers: Unbreak timer rearming
On Fri, Jan 11, 2019 at 5:36 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> The recent commit which prevented a division by 0 issue in the alarm timer
> code broke posix CPU timers as an unwanted side effect.
> The reason is that the common rearm code checks for timer->it_interval
> being 0 now. What went unnoticed is that the posix cpu timer setup does not
> initialize timer->it_interval as it stores the interval in CPU timer
> specific storage. The reason for the separate storage is historical as the
> posix CPU timers always had a 64bit nanoseconds representation internally
> while timer->it_interval is type ktime_t which used to be a modified
> timespec representation on 32bit machines.
> Instead of reverting the offending commit and fixing the alarmtimer issue
> in the alarmtimer code, store the interval in timer->it_interval at CPU
> timer setup time so the common code check works. This also repairs the
> existing inconistency of the posix CPU timer code which kept a single shot
> timer armed despite of the interval being 0.
> The separate storage can be removed in mainline, but that needs to be a
> separate commit as the current one has to be backported to stable kernels.
> Fixes: 0e334db6bb4b ("posix-timers: Fix division by zero bug")
> Reported-by: H.J. Lu <hjl.tools@xxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> kernel/time/posix-cpu-timers.c | 1 +
> 1 file changed, 1 insertion(+)
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -685,6 +685,7 @@ static int posix_cpu_timer_set(struct k_
> * set up the signal and overrun bookkeeping.
> timer->it.cpu.incr = timespec64_to_ns(&new->it_interval);
> + timer->it_interval = ns_to_ktime(timer->it.cpu.incr);
> * This acts as a modification timestamp for the timer,
I verified that this patch works on 4.19.14 kernel.