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Subject: softirq: Fix unplug deadlock
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 30 Sep 2011 15:59:16 +0200
Subject: [RT] softirq: Fix unplug deadlock
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Fri Sep 30 15:52:14 CEST 2011
If ksoftirqd gets woken during hot-unplug, __thread_do_softirq() will
call pin_current_cpu() which will block on the held cpu_hotplug.lock.
Moving the offline check in __thread_do_softirq() before the
pin_current_cpu() call doesn't work, since the wakeup can happen
before we mark the cpu offline.
So here we have the ksoftirq thread stuck until hotplug finishes, but
then the ksoftirq CPU_DOWN notifier issues kthread_stop() which will
wait for the ksoftirq thread to go away -- while holding the hotplug
lock.
Sort this by delaying the kthread_stop() until CPU_POST_DEAD, which is
outside of the cpu_hotplug.lock, but still serialized by the
cpu_add_remove_lock.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: rostedt <rostedt@goodmis.org>
Cc: Clark Williams <williams@redhat.com>
Link: http://lkml.kernel.org/r/1317391156.12973.3.camel@twins
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/softirq.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
Index: linux-stable/kernel/softirq.c
===================================================================
--- linux-stable.orig/kernel/softirq.c
+++ linux-stable/kernel/softirq.c
@@ -1087,9 +1087,8 @@ static int __cpuinit cpu_callback(struct
int hotcpu = (unsigned long)hcpu;
struct task_struct *p;
- switch (action) {
+ switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
- case CPU_UP_PREPARE_FROZEN:
p = kthread_create_on_node(run_ksoftirqd,
hcpu,
cpu_to_node(hotcpu),
@@ -1102,19 +1101,16 @@ static int __cpuinit cpu_callback(struct
per_cpu(ksoftirqd, hotcpu) = p;
break;
case CPU_ONLINE:
- case CPU_ONLINE_FROZEN:
wake_up_process(per_cpu(ksoftirqd, hotcpu));
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_UP_CANCELED:
- case CPU_UP_CANCELED_FROZEN:
if (!per_cpu(ksoftirqd, hotcpu))
break;
/* Unbind so it can run. Fall thru. */
kthread_bind(per_cpu(ksoftirqd, hotcpu),
cpumask_any(cpu_online_mask));
- case CPU_DEAD:
- case CPU_DEAD_FROZEN: {
+ case CPU_POST_DEAD: {
static const struct sched_param param = {
.sched_priority = MAX_RT_PRIO-1
};
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