5 files changed, 37 insertions, 8 deletions

diff --git a/arch/ia64/kernel/perfmon.c b/arch/ia64/kernel/perfmon.c
index 19d4493c6193..fc8f3509df27 100644
--- a/arch/ia64/kernel/perfmon.c
+++ b/arch/ia64/kernel/perfmon.c
@@ -2626,7 +2626,7 @@ pfm_task_incompatible(pfm_context_t *ctx, struct task_struct *task)
         /*
          * make sure the task is off any CPU
          */
-        wait_task_inactive(task);
+        wait_task_inactive(task, 0);
 
         /* more to come... */
 
@@ -4774,7 +4774,7 @@ recheck:
 
                 UNPROTECT_CTX(ctx, flags);
 
-                wait_task_inactive(task);
+                wait_task_inactive(task, 0);
 
                 PROTECT_CTX(ctx, flags);
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index a95d84d0da95..f59318a0099b 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1882,9 +1882,13 @@ extern void set_task_comm(struct task_struct *tsk, char *from);
 extern char *get_task_comm(char *to, struct task_struct *tsk);
 
 #ifdef CONFIG_SMP
-extern void wait_task_inactive(struct task_struct * p);
+extern unsigned long wait_task_inactive(struct task_struct *, long match_state);
 #else
-#define wait_task_inactive(p)   do { } while (0)
+static inline unsigned long wait_task_inactive(struct task_struct *p,
+                                               long match_state)
+{
+        return 1;
+}
 #endif
 
 #define next_task(p)    list_entry(rcu_dereference((p)->tasks.next), struct task_struct, tasks)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 6111c27491b1..96cff2f8710b 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -176,7 +176,7 @@ void kthread_bind(struct task_struct *k, unsigned int cpu)
                 return;
         }
         /* Must have done schedule() in kthread() before we set_task_cpu */
-        wait_task_inactive(k);
+        wait_task_inactive(k, 0);
         set_task_cpu(k, cpu);
         k->cpus_allowed = cpumask_of_cpu(cpu);
         k->rt.nr_cpus_allowed = 1;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 8392a9da6450..082b3fcb32a0 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -107,7 +107,7 @@ int ptrace_check_attach(struct task_struct *child, int kill)
         read_unlock(&tasklist_lock);
 
         if (!ret && !kill)
-                wait_task_inactive(child);
+                ret = wait_task_inactive(child, TASK_TRACED) ? 0 : -ESRCH;
 
         /* All systems go.. */
         return ret;
diff --git a/kernel/sched.c b/kernel/sched.c
index fde1a1026359..0236958addcb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1867,16 +1867,24 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *
+ * If @match_state is nonzero, it's the @p->state value just checked and
+ * not expected to change.  If it changes, i.e. @p might have woken up,
+ * then return zero.  When we succeed in waiting for @p to be off its CPU,
+ * we return a positive number (its total switch count).  If a second call
+ * a short while later returns the same number, the caller can be sure that
+ * @p has remained unscheduled the whole time.
+ *
  * The caller must ensure that the task *will* unschedule sometime soon,
  * else this function might spin for a *long* time. This function can't
  * be called with interrupts off, or it may introduce deadlock with
  * smp_call_function() if an IPI is sent by the same process we are
  * waiting to become inactive.
  */
-void wait_task_inactive(struct task_struct *p)
+unsigned long wait_task_inactive(struct task_struct *p, long match_state)
 {
         unsigned long flags;
         int running, on_rq;
+        unsigned long ncsw;
         struct rq *rq;
 
         for (;;) {
@@ -1899,8 +1907,11 @@ void wait_task_inactive(struct task_struct *p)
                  * return false if the runqueue has changed and p
                  * is actually now running somewhere else!
                  */
-                while (task_running(rq, p))
+                while (task_running(rq, p)) {
+                        if (match_state && unlikely(p->state != match_state))
+                                return 0;
                         cpu_relax();
+                }
 
                 /*
                  * Ok, time to look more closely! We need the rq
@@ -1910,9 +1921,21 @@ void wait_task_inactive(struct task_struct *p)
                 rq = task_rq_lock(p, &flags);
                 running = task_running(rq, p);
                 on_rq = p->se.on_rq;
+                ncsw = 0;
+                if (!match_state || p->state == match_state) {
+                        ncsw = p->nivcsw + p->nvcsw;
+                        if (unlikely(!ncsw))
+                                ncsw = 1;
+                }
                 task_rq_unlock(rq, &flags);
 
                 /*
+                 * If it changed from the expected state, bail out now.
+                 */
+                if (unlikely(!ncsw))
+                        break;
+
+                /*
                  * Was it really running after all now that we
                  * checked with the proper locks actually held?
                  *
@@ -1944,6 +1967,8 @@ void wait_task_inactive(struct task_struct *p)
                  */
                 break;
         }
+
+        return ncsw;
 }
 
 /***