* Mike Galbraith | 2016-04-08 18:49:28 [+0200]:
>On Fri, 2016-04-08 at 16:51 +0200, Sebastian Andrzej Siewior wrote:
>
>> Is there anything you can hand me over?
>
>Sure, I'll send it offline (yup, that proud of my scripting;)
>
> -Mike
take 2. There is this else case in pin_current_cpu() where I take
hp_lock. I didn't manage to get in there. So I *think* we can get rid of
the lock now. Since there is no lock (or will be) we can drop the whole
`do_mig_dis' checking and do the migrate_disable() _after_ we obtained
the lock. We were not able to do so due to the lock hp_lock.
And with this, I didn't manage to triger the lockup you had with
futextest.
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f9a0f2b540f1..b0f786274025 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1492,7 +1492,7 @@ struct task_struct {
#ifdef CONFIG_COMPAT_BRK
unsigned brk_randomized:1;
#endif
-
+ unsigned mig_away :1;
unsigned long atomic_flags; /* Flags needing atomic access. */
struct restart_block restart_block;
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 8edd3c716092..3a1ee02ba3ab 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -30,6 +30,10 @@
/* Serializes the updates to cpu_online_mask, cpu_present_mask */
static DEFINE_MUTEX(cpu_add_remove_lock);
+static DEFINE_SPINLOCK(cpumask_lock);
+static cpumask_var_t mig_cpumask;
+static cpumask_var_t mig_cpumask_org;
+
/*
* The following two APIs (cpu_maps_update_begin/done) must be used when
* attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
@@ -120,6 +124,8 @@ struct hotplug_pcp {
* state.
*/
spinlock_t lock;
+ cpumask_var_t cpumask;
+ cpumask_var_t cpumask_org;
#else
struct mutex mutex;
#endif
@@ -158,9 +164,30 @@ void pin_current_cpu(void)
return;
}
if (hp->grab_lock) {
+ int cpu;
+
+ cpu = smp_processor_id();
preempt_enable();
- hotplug_lock(hp);
- hotplug_unlock(hp);
+ if (cpu != raw_smp_processor_id())
+ goto retry;
+
+ current->mig_away = 1;
+ rt_spin_lock__no_mg(&cpumask_lock);
+
+ /* DOWN */
+ cpumask_copy(mig_cpumask_org, tsk_cpus_allowed(current));
+ cpumask_andnot(mig_cpumask, cpu_online_mask, cpumask_of(cpu));
+ set_cpus_allowed_ptr(current, mig_cpumask);
+
+ if (cpu == raw_smp_processor_id()) {
+ /* BAD */
+ hotplug_lock(hp);
+ hotplug_unlock(hp);
+ }
+ set_cpus_allowed_ptr(current, mig_cpumask_org);
+ current->mig_away = 0;
+ rt_spin_unlock__no_mg(&cpumask_lock);
+
} else {
preempt_enable();
/*
@@ -800,7 +827,13 @@ static struct notifier_block smpboot_thread_notifier = {
void smpboot_thread_init(void)
{
+ bool ok;
+
register_cpu_notifier(&smpboot_thread_notifier);
+ ok = alloc_cpumask_var(&mig_cpumask, GFP_KERNEL);
+ BUG_ON(!ok);
+ ok = alloc_cpumask_var(&mig_cpumask_org, GFP_KERNEL);
+ BUG_ON(!ok);
}
/* Requires cpu_add_remove_lock to be held */
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 66971005cc12..b5e5e6a15278 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -930,13 +930,13 @@ static inline void rt_spin_lock_fastlock(struct rt_mutex
*lock,
{
might_sleep_no_state_check();
- if (do_mig_dis)
+ if (do_mig_dis && 0)
migrate_disable();
if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
rt_mutex_deadlock_account_lock(lock, current);
else
- slowfn(lock, do_mig_dis);
+ slowfn(lock, false);
}
static inline void rt_spin_lock_fastunlock(struct rt_mutex *lock,
@@ -1125,12 +1125,14 @@ void __lockfunc rt_spin_lock(spinlock_t *lock)
{
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock, true);
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
+ migrate_disable();
}
EXPORT_SYMBOL(rt_spin_lock);
void __lockfunc __rt_spin_lock(struct rt_mutex *lock)
{
rt_spin_lock_fastlock(lock, rt_spin_lock_slowlock, true);
+ migrate_disable();
}
EXPORT_SYMBOL(__rt_spin_lock);
@@ -1145,6 +1147,7 @@ void __lockfunc rt_spin_lock_nested(spinlock_t *lock, int
subclass)
{
spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock, true);
+ migrate_disable();
}
EXPORT_SYMBOL(rt_spin_lock_nested);
#endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index da96d97f3d79..0eb7496870bd 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3369,6 +3369,9 @@ static inline void sched_submit_work(struct task_struct
*tsk)
{
if (!tsk->state)
return;
+
+ if (tsk->mig_away)
+ return;
/*
* If a worker went to sleep, notify and ask workqueue whether
* it wants to wake up a task to maintain concurrency.
--
2.8.0.rc3
Sebastian
