Fix clock_was_set so it is safe to call from atomic

Backport for 3.0.36

NOTE:This is a prerequisite patch that's required to
address the widely observed leap-second related futex/hrtimer
issues.

Currently clock_was_set() is unsafe to be called from atomic
context, as it calls on_each_cpu(). This causes problems when
we need to adjust the time from update_wall_time().

To fix this, introduce a work_struct so if we're in_atomic,
we can schedule work to do the necessary update after we're
out of the atomic section.

CC: Prarit Bhargava <prarit@redhat.com>
CC: stable@vger.kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 2043c08d36c89d44731fb70ff01679816704f3a0..c5833ae994f6739aa281dfd2dd80db6bf311a359 100644 (file)
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -746,7 +746,7 @@ static inline void retrigger_next_event(void *arg) { }
  * resolution timer interrupts. On UP we just disable interrupts and
  * call the high resolution interrupt code.
  */
-void clock_was_set(void)
+static void do_clock_was_set(struct work_struct *work)
 {
 #ifdef CONFIG_HIGH_RES_TIMERS
        /* Retrigger the CPU local events everywhere */
@@ -754,6 +754,20 @@ void clock_was_set(void)
 #endif
        timerfd_clock_was_set();
 }
+static DECLARE_WORK(clock_was_set_work, do_clock_was_set);
+
+void clock_was_set(void)
+{
+       /*
+        * We can't call on_each_cpu() from atomic context,
+        * so if we're in_atomic, schedule the clock_was_set
+        * for later.
+        */
+       if (in_atomic())
+               schedule_work(&clock_was_set_work);
+       else
+               do_clock_was_set(NULL);
+}
 
 /*
  * During resume we might have to reprogram the high resolution timer