93 lines
2.8 KiB
Diff
93 lines
2.8 KiB
Diff
|
From 99a3c702fadd5c5185b9b626f8eaa3eb7b965d6f Mon Sep 17 00:00:00 2001
|
||
|
|
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
||
|
|
Date: Fri, 7 Jun 2013 22:37:06 +0200
|
||
|
|
Subject: [PATCH 280/365] kernel/cpu: fix cpu down problem if kthread's cpu is
|
||
|
|
going down
|
||
|
|
|
||
|
|
If kthread is pinned to CPUx and CPUx is going down then we get into
|
||
|
|
trouble:
|
||
|
|
- first the unplug thread is created
|
||
|
|
- it will set itself to hp->unplug. As a result, every task that is
|
||
|
|
going to take a lock, has to leave the CPU.
|
||
|
|
- the CPU_DOWN_PREPARE notifier are started. The worker thread will
|
||
|
|
start a new process for the "high priority worker".
|
||
|
|
Now kthread would like to take a lock but since it can't leave the CPU
|
||
|
|
it will never complete its task.
|
||
|
|
|
||
|
|
We could fire the unplug thread after the notifier but then the cpu is
|
||
|
|
no longer marked "online" and the unplug thread will run on CPU0 which
|
||
|
|
was fixed before :)
|
||
|
|
|
||
|
|
So instead the unplug thread is started and kept waiting until the
|
||
|
|
notfier complete their work.
|
||
|
|
|
||
|
|
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
|
||
|
|
---
|
||
|
|
kernel/cpu.c | 15 +++++++++++++--
|
||
|
|
1 file changed, 13 insertions(+), 2 deletions(-)
|
||
|
|
|
||
|
|
diff --git a/kernel/cpu.c b/kernel/cpu.c
|
||
|
|
index 06d5e5dc3448..1fbc7dd95ccc 100644
|
||
|
|
--- a/kernel/cpu.c
|
||
|
|
+++ b/kernel/cpu.c
|
||
|
|
@@ -267,6 +267,7 @@ struct hotplug_pcp {
|
||
|
|
int refcount;
|
||
|
|
int grab_lock;
|
||
|
|
struct completion synced;
|
||
|
|
+ struct completion unplug_wait;
|
||
|
|
#ifdef CONFIG_PREEMPT_RT_FULL
|
||
|
|
/*
|
||
|
|
* Note, on PREEMPT_RT, the hotplug lock must save the state of
|
||
|
|
@@ -370,6 +371,7 @@ static int sync_unplug_thread(void *data)
|
||
|
|
{
|
||
|
|
struct hotplug_pcp *hp = data;
|
||
|
|
|
||
|
|
+ wait_for_completion(&hp->unplug_wait);
|
||
|
|
preempt_disable();
|
||
|
|
hp->unplug = current;
|
||
|
|
wait_for_pinned_cpus(hp);
|
||
|
|
@@ -435,6 +437,14 @@ static void __cpu_unplug_sync(struct hotplug_pcp *hp)
|
||
|
|
wait_for_completion(&hp->synced);
|
||
|
|
}
|
||
|
|
|
||
|
|
+static void __cpu_unplug_wait(unsigned int cpu)
|
||
|
|
+{
|
||
|
|
+ struct hotplug_pcp *hp = &per_cpu(hotplug_pcp, cpu);
|
||
|
|
+
|
||
|
|
+ complete(&hp->unplug_wait);
|
||
|
|
+ wait_for_completion(&hp->synced);
|
||
|
|
+}
|
||
|
|
+
|
||
|
|
/*
|
||
|
|
* Start the sync_unplug_thread on the target cpu and wait for it to
|
||
|
|
* complete.
|
||
|
|
@@ -458,6 +468,7 @@ static int cpu_unplug_begin(unsigned int cpu)
|
||
|
|
tell_sched_cpu_down_begin(cpu);
|
||
|
|
|
||
|
|
init_completion(&hp->synced);
|
||
|
|
+ init_completion(&hp->unplug_wait);
|
||
|
|
|
||
|
|
hp->sync_tsk = kthread_create(sync_unplug_thread, hp, "sync_unplug/%d", cpu);
|
||
|
|
if (IS_ERR(hp->sync_tsk)) {
|
||
|
|
@@ -473,8 +484,7 @@ static int cpu_unplug_begin(unsigned int cpu)
|
||
|
|
* wait for tasks that are going to enter these sections and
|
||
|
|
* we must not have them block.
|
||
|
|
*/
|
||
|
|
- __cpu_unplug_sync(hp);
|
||
|
|
-
|
||
|
|
+ wake_up_process(hp->sync_tsk);
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
@@ -1205,6 +1215,7 @@ static int takedown_cpu(unsigned int cpu)
|
||
|
|
struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
|
||
|
|
int err;
|
||
|
|
|
||
|
|
+ __cpu_unplug_wait(cpu);
|
||
|
|
/* Park the smpboot threads */
|
||
|
|
kthread_park(per_cpu_ptr(&cpuhp_state, cpu)->thread);
|
||
|
|
|
||
|
|
--
|
||
|
|
2.28.0
|
||
|
|
|