The patch titled
time: avoid possible endless loop when using jiffies clocksource and ONESHOT mode clockevent
has been added to the -mm tree. Its filename is
time-avoid-possible-endless-loop-when-using-jiffies-clocksource-and-oneshot-mode-clockevent.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: time: avoid possible endless loop when using jiffies clocksource and ONESHOT mode clockevent
From: john stultz <johnstul@xxxxxxxxxx>
Avoid an endless loop issue by requiring that a highres valid clocksource
be installed before we call tick_periodic() in a loop when using ONESHOT
mode. The result is we will only increment jiffies once per interrupt
until a continuous hardware clocksource is available.
Without this, we can run into a endless loop, where each cycle through the
loop, jiffies is updated which increments time by tick_period or more (due
to clock steering), which can cause the event programming to think the
next event was before the newly incremented time and fail causing
tick_periodic() to be called again and the whole process loops forever.
Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Roman Zippel <zippel@xxxxxxxxxxxxxx>
Cc: Frans Pop <elendil@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/time/tick-common.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff -puN kernel/time/tick-common.c~avoid-possible-endless-loop-when-using-jiffies-clocksource-and-oneshot-mode-clockevent kernel/time/tick-common.c
--- a/kernel/time/tick-common.c~avoid-possible-endless-loop-when-using-jiffies-clocksource-and-oneshot-mode-clockevent
+++ a/kernel/time/tick-common.c
@@ -94,7 +94,17 @@ void tick_handle_periodic(struct clock_e
for (;;) {
if (!clockevents_program_event(dev, next, ktime_get()))
return;
- tick_periodic(cpu);
+ /*
+ * Have to be careful here. If we're in oneshot mode,
+ * before we call tick_periodic() in a loop, we need
+ * to be sure we're using a real hardware clocksource.
+ * Otherwise we could get trapped in an infinite
+ * loop, as the tick_periodic() increments jiffies,
+ * when then will increment time, posibly causing
+ * the loop to trigger again and again.
+ */
+ if (timekeeping_valid_for_hres())
+ tick_periodic(cpu);
next = ktime_add(next, tick_period);
}
}
_
Patches currently in -mm which might be from johnstul@xxxxxxxxxx are
clocksource-pass-clocksource-to-read-callback.patch
clocksource-add-enable-and-disable-callbacks.patch
clocksource-sanity-check-sysfs-clocksource-changes.patch
time-move-calc_load-call-out-from-xtime_lock-protection.patch
time-avoid-possible-endless-loop-when-using-jiffies-clocksource-and-oneshot-mode-clockevent.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
