4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> commit 93ad0fc088c5b4631f796c995bdd27a082ef33a6 upstream. 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: John Stultz <john.stultz@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r/20190111133500.840117406@xxxxxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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,