The patch titled
Prevent going idle with softirq pending
has been added to the -mm tree. Its filename is
prevent-going-idle-with-softirq-pending.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: Prevent going idle with softirq pending
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
The NOHZ patch contains a check for softirqs pending when a CPU goes idle.
The BUG is unrelated to NOHZ, it just was made visible by the NOHZ patch.
The BUG showed up mainly on P4 / hyperthreading enabled machines which lead
the investigations into the wrong direction in the first place. The real
cause is in cond_resched_softirq():
cond_resched_softirq() is enabling softirqs without invoking the softirq
daemon when softirqs are pending. This leads to the warning message in the
NOHZ idle code:
t1 runs softirq disabled code on CPU#0
interrupt happens, softirq is raised, but deferred (softirqs disabled)
t1 calls cond_resched_softirq()
enables softirqs via _local_bh_enable()
calls schedule()
t2 runs
t1 is migrated to CPU#1
t2 is done and invokes idle()
NOHZ detects the pending softirq
Fix: change _local_bh_enable() to local_bh_enable() so the softirq
daemon is invoked.
Thanks to Anant Nitya for debugging this with great patience !
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/sched.c | 4 +---
1 files changed, 1 insertion(+), 3 deletions(-)
diff -puN kernel/sched.c~prevent-going-idle-with-softirq-pending kernel/sched.c
--- a/kernel/sched.c~prevent-going-idle-with-softirq-pending
+++ a/kernel/sched.c
@@ -4775,9 +4775,7 @@ int __sched cond_resched_softirq(void)
BUG_ON(!in_softirq());
if (need_resched() && system_state == SYSTEM_RUNNING) {
- raw_local_irq_disable();
- _local_bh_enable();
- raw_local_irq_enable();
+ local_bh_enable();
__cond_resched();
local_bh_disable();
return 1;
_
Patches currently in -mm which might be from tglx@xxxxxxxxxxxxx are
ignore-bogus-acpi-info-for-offline-cpus.patch
nohz-rate-limit-the-local-softirq-pending-warning-output.patch
drm-spinlock-initializer-cleanup.patch
s390-spinlock-initializer-cleanup.patch
i386-hpet-check-if-the-counter-works.patch
doc-clocksources.patch
prevent-going-idle-with-softirq-pending.patch
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