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.

By having p->sched_class and p->cpus_allowed serialized by p->pi_lock,
we prepare the way to call select_task_rq() without holding rq->lock.

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110405152728.990364093@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 16 insertions, 21 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index dece28e505c9..d398f2f0a3c9 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2340,7 +2340,7 @@ EXPORT_SYMBOL_GPL(kick_process);
 
 #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)
 {
@@ -2373,7 +2373,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 }
 
 /*
- * 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)
@@ -2499,7 +2499,8 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
         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;
 
@@ -2557,7 +2558,8 @@ out_running:
         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;
@@ -4694,6 +4696,8 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
 
         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);
@@ -5317,7 +5321,6 @@ long sched_getaffinity(pid_t pid, struct cpumask *mask)
 {
         struct task_struct *p;
         unsigned long flags;
-        struct rq *rq;
         int retval;
 
         get_online_cpus();
@@ -5332,9 +5335,9 @@ long sched_getaffinity(pid_t pid, struct cpumask *mask)
         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();
@@ -5882,18 +5885,8 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
         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;
@@ -5921,13 +5914,15 @@ again:
         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;
 }