[Xen-devel] [PATCH 106/106] hrtimers: Move SMP function call to thread context

[Luis Henriques <luis.henriques@xxxxxxxxxxxxx>]

3.5.7.18 -stable review patch.  If anyone has any objections, please let me 
know.

------------------

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

commit 5ec2481b7b47a4005bb446d176e5d0257400c77d upstream.

smp_call_function_* must not be called from softirq context.

But clock_was_set() which calls on_each_cpu() is called from softirq
context to implement a delayed clock_was_set() for the timer interrupt
handler. Though that almost never gets invoked. A recent change in the
resume code uses the softirq based delayed clock_was_set to support
Xens resume mechanism.

linux-next contains a new warning which warns if smp_call_function_*
is called from softirq context which gets triggered by that Xen
change.

Fix this by moving the delayed clock_was_set() call to a work context.

Reported-and-tested-by: Artem Savkov <artem.savkov@xxxxxxxxx>
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>,
Cc: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
[ luis: backported to 3.5: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
 kernel/hrtimer.c | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 60f7e32..a57ef25 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -707,17 +707,20 @@ static int hrtimer_switch_to_hres(void)
        return 1;
 }
 
+static void clock_was_set_work(struct work_struct *work)
+{
+       clock_was_set();
+}
+
+static DECLARE_WORK(hrtimer_work, clock_was_set_work);
+
 /*
- * Called from timekeeping code to reprogramm the hrtimer interrupt
- * device. If called from the timer interrupt context we defer it to
- * softirq context.
+ * Called from timekeeping and resume code to reprogramm the hrtimer
+ * interrupt device on all cpus.
  */
 void clock_was_set_delayed(void)
 {
-       struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
-
-       cpu_base->clock_was_set = 1;
-       __raise_softirq_irqoff(HRTIMER_SOFTIRQ);
+       schedule_work(&hrtimer_work);
 }
 
 #else
@@ -766,8 +769,10 @@ void hrtimers_resume(void)
        WARN_ONCE(!irqs_disabled(),
                  KERN_INFO "hrtimers_resume() called with IRQs enabled!");
 
+       /* Retrigger on the local CPU */
        retrigger_next_event(NULL);
-       timerfd_clock_was_set();
+       /* And schedule a retrigger for all others */
+       clock_was_set_delayed();
 }
 
 static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)
@@ -1416,13 +1421,6 @@ void hrtimer_peek_ahead_timers(void)
 
 static void run_hrtimer_softirq(struct softirq_action *h)
 {
-       struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
-
-       if (cpu_base->clock_was_set) {
-               cpu_base->clock_was_set = 0;
-               clock_was_set();
-       }
-
        hrtimer_peek_ahead_timers();
 }
 
-- 
1.8.3.2


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