| 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 |
| }; |