4.20-stable review patch. If anyone has any objections, please let me know.
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From: Thomas Gleixner tglx@linutronix.de
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@gmail.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: John Stultz john.stultz@linaro.org Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20190111133500.840117406@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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,