The patch titled
Ignore stolen time in the softlockup watchdog
has been added to the -mm tree. Its filename is
ignore-stolen-time-in-the-softlockup-watchdog.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: Ignore stolen time in the softlockup watchdog
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
The softlockup watchdog is currently a nuisance in a virtual machine, since
the whole system could have the CPU stolen from it for a long period of
time. While it would be unlikely for a guest domain to be denied timer
interrupts for over 10s, it could happen and any softlockup message would
be completely spurious.
Earlier I proposed that sched_clock() return time in unstolen nanoseconds,
which is how Xen and VMI currently implement it. If the softlockup
watchdog uses sched_clock() to measure time, it would automatically ignore
stolen time, and therefore only report when the guest itself locked up.
When running native, sched_clock() returns real-time nanoseconds, so the
behaviour would be unchanged.
Note that sched_clock() used this way is inherently per-cpu, so this patch
makes sure that the per-processor watchdog thread initialized its own
timestamp.
(akpm: this patch, when combined with Andi's sched_clock() rewrite causes six
mysterious errors in the locking API selftests. We don't know where the
problem lies, but we want to find out).
Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>
Cc: Zachary Amsden <zach@xxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Dan Hecht <dhecht@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Chris Lalancette <clalance@xxxxxxxxxx>
Cc: Rick Lindsley <ricklind@xxxxxxxxxx>
Cc: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/softlockup.c | 37 ++++++++++++++++++++++++++++++-------
1 file changed, 30 insertions(+), 7 deletions(-)
diff -puN kernel/softlockup.c~ignore-stolen-time-in-the-softlockup-watchdog kernel/softlockup.c
--- a/kernel/softlockup.c~ignore-stolen-time-in-the-softlockup-watchdog
+++ a/kernel/softlockup.c
@@ -34,9 +34,19 @@ static struct notifier_block panic_block
.notifier_call = softlock_panic,
};
+/*
+ * Returns seconds, approximately. We don't need nanosecond
+ * resolution, and we don't need to waste time with a big divide when
+ * 2^30ns == 1.074s.
+ */
+static unsigned long get_timestamp(void)
+{
+ return sched_clock() >> 30; /* 2^30 ~= 10^9 */
+}
+
void touch_softlockup_watchdog(void)
{
- __raw_get_cpu_var(touch_timestamp) = jiffies;
+ __raw_get_cpu_var(touch_timestamp) = get_timestamp();
}
EXPORT_SYMBOL(touch_softlockup_watchdog);
@@ -47,10 +57,18 @@ EXPORT_SYMBOL(touch_softlockup_watchdog)
void softlockup_tick(void)
{
int this_cpu = smp_processor_id();
- unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu);
+ unsigned long touch_timestamp = __get_cpu_var(touch_timestamp);
+ unsigned long print_timestamp;
+ unsigned long now;
- /* prevent double reports: */
- if (per_cpu(print_timestamp, this_cpu) == touch_timestamp ||
+ /* watchdog task hasn't updated timestamp yet */
+ if (touch_timestamp == 0)
+ return;
+
+ print_timestamp = __get_cpu_var(print_timestamp);
+
+ /* report at most once a second */
+ if (print_timestamp < (touch_timestamp + 1) ||
did_panic ||
!per_cpu(watchdog_task, this_cpu))
return;
@@ -61,12 +79,14 @@ void softlockup_tick(void)
return;
}
+ now = get_timestamp();
+
/* Wake up the high-prio watchdog task every second: */
- if (time_after(jiffies, touch_timestamp + HZ))
+ if (now > (touch_timestamp + 1))
wake_up_process(per_cpu(watchdog_task, this_cpu));
/* Warn about unreasonable 10+ seconds delays: */
- if (time_after(jiffies, touch_timestamp + 10*HZ)) {
+ if (now > (touch_timestamp + 10)) {
per_cpu(print_timestamp, this_cpu) = touch_timestamp;
spin_lock(&print_lock);
@@ -87,6 +107,9 @@ static int watchdog(void * __bind_cpu)
sched_setscheduler(current, SCHED_FIFO, ¶m);
current->flags |= PF_NOFREEZE;
+ /* initialize timestamp */
+ touch_softlockup_watchdog();
+
/*
* Run briefly once per second to reset the softlockup timestamp.
* If this gets delayed for more than 10 seconds then the
@@ -118,7 +141,7 @@ cpu_callback(struct notifier_block *nfb,
printk("watchdog for %i failed\n", hotcpu);
return NOTIFY_BAD;
}
- per_cpu(touch_timestamp, hotcpu) = jiffies;
+ per_cpu(touch_timestamp, hotcpu) = 0;
per_cpu(watchdog_task, hotcpu) = p;
kthread_bind(p, hotcpu);
break;
_
Patches currently in -mm which might be from jeremy@xxxxxxxx are
revert-x86_64-mm-account-for-module-percpu-space-separately-from-kernel-percpu.patch
add-apply_to_page_range-which-applies-a-function-to-a-pte-range.patch
rename-the-parainstructions-symbols-to-be-consistent-with-the-others.patch
rename-the-parainstructions-symbols-to-be-consistent-with-the-others-fix.patch
allow-boot-time-disable-of-paravirt_ops-patching.patch
i386-map-enough-initial-memory-to-create-lowmem-mappings.patch
i386-map-enough-initial-memory-to-create-lowmem-mappings-fix.patch
mm-only-i386-for-debugging-make-the-initial-page-table-setup-less-forgiving.patch
maps2-uninline-some-functions-in-the-page-walker.patch
maps2-eliminate-the-pmd_walker-struct-in-the-page-walker.patch
maps2-remove-vma-from-args-in-the-page-walker.patch
maps2-propagate-errors-from-callback-in-page-walker.patch
maps2-add-callbacks-for-each-level-to-page-walker.patch
maps2-move-the-page-walker-code-to-lib.patch
maps2-move-the-page-walker-code-to-lib-fix.patch
maps2-simplify-interdependence-of-proc-pid-maps-and-smaps.patch
maps2-move-clear_refs-code-to-task_mmuc.patch
maps2-regroup-task_mmu-by-interface.patch
maps2-make-proc-pid-smaps-optional-under-config_embedded.patch
maps2-make-proc-pid-clear_refs-option-under-config_embedded.patch
maps2-add-proc-pid-pagemap-interface.patch
maps2-add-proc-kpagemap-interface.patch
fixes-and-cleanups-for-earlyprintk-aka-boot-console.patch
ignore-stolen-time-in-the-softlockup-watchdog.patch
ignore-stolen-time-in-the-softlockup-watchdog-fix.patch
add-touch_all_softlockup_watchdogs.patch
clean-up-elf-note-generation.patch
deflate-stack-usage-in-lib-inflatec.patch
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