stop_machine: Store task reference in a separate per cpu variable

To allow the stopper thread being managed by the smpboot thread
infrastructure separate out the task storage from the stopper data
structure.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Arjan van de Veen <arjan@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Richard Weinberger <rw@linutronix.de>
Cc: Magnus Damm <magnus.damm@gmail.com>
Link: http://lkml.kernel.org/r/20130131120741.626690384@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 16 insertions, 16 deletions

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 2f194e965715..aaac68c5c3be 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -37,10 +37,10 @@ struct cpu_stopper {
         spinlock_t              lock;
         bool                    enabled;        /* is this stopper enabled? */
         struct list_head        works;          /* list of pending works */
-        struct task_struct      *thread;        /* stopper thread */
 };
 
 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
+static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);
 static bool stop_machine_initialized = false;
 
 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
@@ -62,16 +62,18 @@ static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
 }
 
 /* queue @work to @stopper.  if offline, @work is completed immediately */
-static void cpu_stop_queue_work(struct cpu_stopper *stopper,
-                                struct cpu_stop_work *work)
+static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 {
+        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
+        struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
+
         unsigned long flags;
 
         spin_lock_irqsave(&stopper->lock, flags);
 
         if (stopper->enabled) {
                 list_add_tail(&work->list, &stopper->works);
-                wake_up_process(stopper->thread);
+                wake_up_process(p);
         } else
                 cpu_stop_signal_done(work->done, false);
 
@@ -108,7 +110,7 @@ int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
         struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
 
         cpu_stop_init_done(&done, 1);
-        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
+        cpu_stop_queue_work(cpu, &work);
         wait_for_completion(&done.completion);
         return done.executed ? done.ret : -ENOENT;
 }
@@ -130,7 +132,7 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
                         struct cpu_stop_work *work_buf)
 {
         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
-        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
+        cpu_stop_queue_work(cpu, work_buf);
 }
 
 /* static data for stop_cpus */
@@ -159,8 +161,7 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
          */
         preempt_disable();
         for_each_cpu(cpu, cpumask)
-                cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
-                                    &per_cpu(stop_cpus_work, cpu));
+                cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
         preempt_enable();
 }
 
@@ -304,12 +305,11 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 {
         unsigned int cpu = (unsigned long)hcpu;
         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
-        struct task_struct *p;
+        struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
 
         switch (action & ~CPU_TASKS_FROZEN) {
         case CPU_UP_PREPARE:
-                BUG_ON(stopper->thread || stopper->enabled ||
-                       !list_empty(&stopper->works));
+                BUG_ON(p || stopper->enabled || !list_empty(&stopper->works));
                 p = kthread_create_on_node(cpu_stopper_thread,
                                            stopper,
                                            cpu_to_node(cpu),
@@ -319,12 +319,12 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
                 get_task_struct(p);
                 kthread_bind(p, cpu);
                 sched_set_stop_task(cpu, p);
-                stopper->thread = p;
+                per_cpu(cpu_stopper_task, cpu) = p;
                 break;
 
         case CPU_ONLINE:
                 /* strictly unnecessary, as first user will wake it */
-                wake_up_process(stopper->thread);
+                wake_up_process(p);
                 /* mark enabled */
                 spin_lock_irq(&stopper->lock);
                 stopper->enabled = true;
@@ -339,7 +339,7 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 
                 sched_set_stop_task(cpu, NULL);
                 /* kill the stopper */
-                kthread_stop(stopper->thread);
+                kthread_stop(p);
                 /* drain remaining works */
                 spin_lock_irq(&stopper->lock);
                 list_for_each_entry(work, &stopper->works, list)
@@ -347,8 +347,8 @@ static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
                 stopper->enabled = false;
                 spin_unlock_irq(&stopper->lock);
                 /* release the stopper */
-                put_task_struct(stopper->thread);
-                stopper->thread = NULL;
+                put_task_struct(p);
+                per_cpu(cpu_stopper_task, cpu) = NULL;
                 break;
         }
 #endif