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Old 07-05-2012, 04:08 PM
Brad Figg
Default (pre-upstream) hrtimer: Fix clock_was_set so it is safe to call from irq context

From: John Stultz <johnstul@us.ibm.com>

BugLink: http://bugs.launchpad.net/bugs/1020285

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

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

To fix this, if clock_was_set is called when irqs are
disabled, we schedule a timer to fire for immedately after
we're out of interrupt context to then notify the hrtimer

CC: Prarit Bhargava <prarit@redhat.com>
CC: stable@vger.kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>
CC: linux@openhuawei.org
Reported-by: Jan Engelhardt <jengelh@inai.de>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Brad Figg <brad.figg@canonical.com>
kernel/hrtimer.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index ae34bf5..d730678 100644
--- 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(unsigned long data)
/* Retrigger the CPU local events everywhere */
@@ -755,6 +755,21 @@ void clock_was_set(void)

+static DEFINE_TIMER(clock_was_set_timer, do_clock_was_set , 0, 0);
+void clock_was_set(void)
+ /*
+ * We can't call on_each_cpu() from irq context,
+ * so if irqs are disabled , schedule the clock_was_set
+ * via a timer_list timer for right after.
+ */
+ if (irqs_disabled())
+ mod_timer(&clock_was_set_timer, jiffies);
+ else
+ do_clock_was_set(0);
* During resume we might have to reprogram the high resolution timer
* interrupt (on the local CPU):

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