[PATCH 1/2] [RFC] Fix clock_was_set so it is safe to call from atomic

From: John Stultz
Date: Sun Jul 01 2012 - 14:31:31 EST

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 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@xxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reported-by: Jan Engelhardt <jengelh@xxxxxxx>
Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>
kernel/hrtimer.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index ae34bf5..ee7a98d 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(struct work_struct *work)
/* Retrigger the CPU local events everywhere */
@@ -754,6 +754,20 @@ void clock_was_set(void)
+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

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