The patch titled
generic one-shot bug
has been added to the -mm tree. Its filename is
generic-one-shot-bug.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: generic one-shot bug
From: David Miller <davem@xxxxxxxxxxxxx>
As I suspected, the one-shot code wasn't very well tested and I'd be the
one to debug this thing on sparc64 :-)
When a timer exceeds the timer period, the one-shot handling code does
the following loop:
for (;;) {
ktime_t next = ktime_add(dev->next_event, tick_period);
if (!clockevents_program_event(dev, next, ktime_get()))
return;
tick_periodic(cpu);
}
So it just keeps running tick_periodic() until we "catch up".
Problem is, if clockevents_program_event() gets a "next" time in the past,
the very case where we'll loop, it DOES NOT update dev->next_event. It
returns the error before doing so.
As a result of this, we'll loop forever here, the softlockup watchdog will
trigger, and the system will wedge completely.
I was getting a softlockup and immediate system hang, so to debug this I
kept a history of the last 8 TSC values when tick_periodic() was invoked.
At softlockup trigger, I'd dump the log. And what I saw were TSC deltas
that we so tiny as to be just enough to indicate tick_periodic() was
running in a tight loop :-)
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Acked-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/time/tick-common.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff -puN kernel/time/tick-common.c~generic-one-shot-bug kernel/time/tick-common.c
--- a/kernel/time/tick-common.c~generic-one-shot-bug
+++ a/kernel/time/tick-common.c
@@ -77,6 +77,7 @@ static void tick_periodic(int cpu)
void tick_handle_periodic(struct clock_event_device *dev)
{
int cpu = smp_processor_id();
+ ktime_t next;
tick_periodic(cpu);
@@ -86,12 +87,12 @@ void tick_handle_periodic(struct clock_e
* Setup the next period for devices, which do not have
* periodic mode:
*/
+ next = ktime_add(dev->next_event, tick_period);
for (;;) {
- ktime_t next = ktime_add(dev->next_event, tick_period);
-
if (!clockevents_program_event(dev, next, ktime_get()))
return;
tick_periodic(cpu);
+ next = ktime_add(next, tick_period);
}
}
_
Patches currently in -mm which might be from davem@xxxxxxxxxxxxx are
tick-schedc-build-fix.patch
generic-one-shot-bug.patch
git-net.patch
resend-iphase-64bit-cleanup.patch
simplify-the-stacktrace-code.patch
tg3-use-flush_keventd_work.patch
e1000-use-flush_keventd_work.patch
ipvs-flush-defense_work-before-module-unload.patch
unify-flush_work-flush_work_keventd-and-rename-it-to-cancel_work_sync.patch
atomich-add-atomic64-cmpxchg-xchg-and-add_unless-to-sparc64.patch
local_t-sparc64-cleanup.patch
-
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