migrate-cpu: Prevent migration target from calling schedule() twice

Symptom:
A thread could call schedule() twice.

Cause:
 (1) The migrator raises rescheduling flag
 (2) The thread calls check_need_resched() for other
     reason than the migrate IPI, e.g, response to system call
     offload. And it finds that the flag is set and it's trying to
     call schedule().
 (3) The thread is interrupted by the migrate IPI and it finds that
     the flag is set and calls schedule() in the interrupt context.
 (4) The thread resumes the execution and call schedule()

Solution:
 (1) Reset the rescheduling flag when checking it and it's set
 (2) Set it again if it's decided not to call schedule()

Change-Id: I5376662d0b02ca4ebb29b42732e347f3b82d766d
Refs: #1400

kernel/process.c

@@ -3381,6 +3381,7 @@ void spin_sleep_or_schedule(void)
 		v = get_this_cpu_local_var();
 
 		if (v->flags & CPU_FLAG_NEED_RESCHED || v->runq_len > 1) {
+			v->flags &= ~CPU_FLAG_NEED_RESCHED;
 			do_schedule = 1;
 		}
 
@@ -3406,6 +3407,11 @@ void spin_sleep_or_schedule(void)
 		}
 
 		if (woken) {
+			if (do_schedule) {
+				irqstate = ihk_mc_spinlock_lock(&v->runq_lock);
+				v->flags |= CPU_FLAG_NEED_RESCHED;
+				ihk_mc_spinlock_unlock(&v->runq_lock, irqstate);
+			}
 			return;
 		}
 
@@ -3432,6 +3438,16 @@ void schedule(void)
 	if (cpu_local_var(no_preempt)) {
 		kprintf("%s: WARNING can't schedule() while no preemption, cnt: %d\n",
 			__FUNCTION__, cpu_local_var(no_preempt));
+
+		irqstate = cpu_disable_interrupt_save();
+		ihk_mc_spinlock_lock_noirq(
+			&(get_this_cpu_local_var()->runq_lock));
+		v = get_this_cpu_local_var();
+
+		v->flags |= CPU_FLAG_NEED_RESCHED;
+
+		ihk_mc_spinlock_unlock_noirq(&v->runq_lock);
+		cpu_restore_interrupt(irqstate);
 		return;
 	}
 
@@ -3444,8 +3460,6 @@ void schedule(void)
 	prev = v->current;
 	prevpid = v->prevpid;
 	
-	v->flags &= ~CPU_FLAG_NEED_RESCHED;
-
 	/* All runnable processes are on the runqueue */
 	if (prev && prev != &cpu_local_var(idle)) {
 		list_del(&prev->sched_list);
@@ -3576,7 +3590,6 @@ void schedule(void)
 		/* Have we migrated to another core meanwhile? */
 		if (v != get_this_cpu_local_var()) {
 			v = get_this_cpu_local_var();
-			v->flags &= ~CPU_FLAG_NEED_RESCHED;
 		}
 	}
 	else {
@@ -3610,6 +3623,7 @@ void check_need_resched(void)
 			ihk_mc_spinlock_unlock(&v->runq_lock, irqstate);
 			return;
 		}
+		v->flags &= ~CPU_FLAG_NEED_RESCHED;
 		ihk_mc_spinlock_unlock(&v->runq_lock, irqstate);
 		schedule();
 	}

kernel/syscall.c

@@ -259,6 +259,7 @@ long do_syscall(struct syscall_request *req, int cpu)
 			if (v->flags & CPU_FLAG_NEED_RESCHED ||
 			    v->runq_len > 1 ||
 			    req->number == __NR_sched_setaffinity) {
+				v->flags &= ~CPU_FLAG_NEED_RESCHED;
 				do_schedule = 1;
 			}
 
@@ -285,6 +286,16 @@ long do_syscall(struct syscall_request *req, int cpu)
 				schedule();
 				waitq_finish_wait(&thread->scd_wq, &scd_wq_entry);
 			}
+			else {
+				if (do_schedule) {
+					runq_irqstate =
+						ihk_mc_spinlock_lock(
+							&v->runq_lock);
+					v->flags |= CPU_FLAG_NEED_RESCHED;
+					ihk_mc_spinlock_unlock(
+						&v->runq_lock, runq_irqstate);
+				}
+			}
 
 			cpu_restore_interrupt(flags);
 		}
@@ -4969,6 +4980,7 @@ do_sigsuspend(struct thread *thread, const sigset_t *set)
 			v = get_this_cpu_local_var();
 
 			if (v->flags & CPU_FLAG_NEED_RESCHED) {
+				v->flags &= ~CPU_FLAG_NEED_RESCHED;
 				do_schedule = 1;
 			}
 
@@ -7934,6 +7946,7 @@ SYSCALL_DECLARE(sched_yield)
 	runq_irqstate = ihk_mc_spinlock_lock(&v->runq_lock);
 
 	if (v->flags & CPU_FLAG_NEED_RESCHED || v->runq_len > 1) {
+		v->flags &= ~CPU_FLAG_NEED_RESCHED;
 		do_schedule = 1;
 	}