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Subject[RFC][PATCH 07/17] sched: Serialize p->cpus_allowed and ttwu() using p->pi_lock
Currently p->pi_lock already serializes p->sched_class, also put
p->cpus_allowed and try_to_wake_up() under it, this prepares the way
to do the first part of ttwu() without holding rq->lock.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
kernel/sched.c | 37 ++++++++++++++++---------------------
1 file changed, 16 insertions(+), 21 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2301,7 +2301,7 @@ void task_oncpu_function_call(struct tas

#ifdef CONFIG_SMP
/*
- * ->cpus_allowed is protected by either TASK_WAKING or rq->lock held.
+ * ->cpus_allowed is protected by both rq->lock and p->pi_lock
*/
static int select_fallback_rq(int cpu, struct task_struct *p)
{
@@ -2334,7 +2334,7 @@ static int select_fallback_rq(int cpu, s
}

/*
- * The caller (fork, wakeup) owns TASK_WAKING, ->cpus_allowed is stable.
+ * The caller (fork, wakeup) owns p->pi_lock, ->cpus_allowed is stable.
*/
static inline
int select_task_rq(struct rq *rq, struct task_struct *p, int sd_flags, int wake_flags)
@@ -2450,7 +2450,8 @@ static int try_to_wake_up(struct task_st
this_cpu = get_cpu();

smp_wmb();
- rq = task_rq_lock(p, &flags);
+ raw_spin_lock_irqsave(&p->pi_lock, flags);
+ rq = __task_rq_lock(p);
if (!(p->state & state))
goto out;

@@ -2508,7 +2509,8 @@ static int try_to_wake_up(struct task_st
ttwu_stat(rq, p, cpu, wake_flags);
success = 1;
out:
- task_rq_unlock(rq, &flags);
+ __task_rq_unlock(rq);
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);
put_cpu();

return success;
@@ -4543,6 +4545,8 @@ void rt_mutex_setprio(struct task_struct

BUG_ON(prio < 0 || prio > MAX_PRIO);

+ lockdep_assert_held(&p->pi_lock);
+
rq = task_rq_lock(p, &flags);

trace_sched_pi_setprio(p, prio);
@@ -5150,7 +5154,6 @@ long sched_getaffinity(pid_t pid, struct
{
struct task_struct *p;
unsigned long flags;
- struct rq *rq;
int retval;

get_online_cpus();
@@ -5165,9 +5168,9 @@ long sched_getaffinity(pid_t pid, struct
if (retval)
goto out_unlock;

- rq = task_rq_lock(p, &flags);
+ raw_spin_lock_irqsave(&p->pi_lock, flags);
cpumask_and(mask, &p->cpus_allowed, cpu_online_mask);
- task_rq_unlock(rq, &flags);
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);

out_unlock:
rcu_read_unlock();
@@ -5652,18 +5655,8 @@ int set_cpus_allowed_ptr(struct task_str
unsigned int dest_cpu;
int ret = 0;

- /*
- * Serialize against TASK_WAKING so that ttwu() and wunt() can
- * drop the rq->lock and still rely on ->cpus_allowed.
- */
-again:
- while (task_is_waking(p))
- cpu_relax();
- rq = task_rq_lock(p, &flags);
- if (task_is_waking(p)) {
- task_rq_unlock(rq, &flags);
- goto again;
- }
+ raw_spin_lock_irqsave(&p->pi_lock, flags);
+ rq = __task_rq_lock(p);

if (!cpumask_intersects(new_mask, cpu_active_mask)) {
ret = -EINVAL;
@@ -5691,13 +5684,15 @@ int set_cpus_allowed_ptr(struct task_str
if (migrate_task(p, rq)) {
struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
- task_rq_unlock(rq, &flags);
+ __task_rq_unlock(rq);
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);
stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
tlb_migrate_finish(p->mm);
return 0;
}
out:
- task_rq_unlock(rq, &flags);
+ __task_rq_unlock(rq);
+ raw_spin_unlock_irqrestore(&p->pi_lock, flags);

return ret;
}



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