queue-4.14/posix-cpu-timers-unbreak-timer-rearming.patch

   1 From 93ad0fc088c5b4631f796c995bdd27a082ef33a6 Mon Sep 17 00:00:00 2001
   2 From: Thomas Gleixner <tglx@linutronix.de>
   3 Date: Fri, 11 Jan 2019 14:33:16 +0100
   4 Subject: posix-cpu-timers: Unbreak timer rearming
   5
   6 From: Thomas Gleixner <tglx@linutronix.de>
   7
   8 commit 93ad0fc088c5b4631f796c995bdd27a082ef33a6 upstream.
   9
  10 The recent commit which prevented a division by 0 issue in the alarm timer
  11 code broke posix CPU timers as an unwanted side effect.
  12
  13 The reason is that the common rearm code checks for timer->it_interval
  14 being 0 now. What went unnoticed is that the posix cpu timer setup does not
  15 initialize timer->it_interval as it stores the interval in CPU timer
  16 specific storage. The reason for the separate storage is historical as the
  17 posix CPU timers always had a 64bit nanoseconds representation internally
  18 while timer->it_interval is type ktime_t which used to be a modified
  19 timespec representation on 32bit machines.
  20
  21 Instead of reverting the offending commit and fixing the alarmtimer issue
  22 in the alarmtimer code, store the interval in timer->it_interval at CPU
  23 timer setup time so the common code check works. This also repairs the
  24 existing inconistency of the posix CPU timer code which kept a single shot
  25 timer armed despite of the interval being 0.
  26
  27 The separate storage can be removed in mainline, but that needs to be a
  28 separate commit as the current one has to be backported to stable kernels.
  29
  30 Fixes: 0e334db6bb4b ("posix-timers: Fix division by zero bug")
  31 Reported-by: H.J. Lu <hjl.tools@gmail.com>
  32 Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
  33 Cc: John Stultz <john.stultz@linaro.org>
  34 Cc: Peter Zijlstra <peterz@infradead.org>
  35 Cc: stable@vger.kernel.org
  36 Link: https://lkml.kernel.org/r/20190111133500.840117406@linutronix.de
  37 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  38
  39 ---
  40  kernel/time/posix-cpu-timers.c |    1 +
  41  1 file changed, 1 insertion(+)
  42
  43 --- a/kernel/time/posix-cpu-timers.c
  44 +++ b/kernel/time/posix-cpu-timers.c
  45 @@ -685,6 +685,7 @@ static int posix_cpu_timer_set(struct k_
  46          * set up the signal and overrun bookkeeping.
  47          */
  48         timer->it.cpu.incr = timespec64_to_ns(&new->it_interval);
  49 +       timer->it_interval = ns_to_ktime(timer->it.cpu.incr);
  50
  51         /*
  52          * This acts as a modification timestamp for the timer,