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Commit 246d86b5 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

sched: Simplify the reacquire_kernel_lock() logic 



- Contrary to what 6d558c3a says, there is no need to reload
  prev = rq->curr after the context switch. You always schedule
  back to where you came from, prev must be equal to current
  even if cpu/rq was changed.

- This also means reacquire_kernel_lock() can use prev instead
  of current.

- No need to reassign switch_count if reacquire_kernel_lock()
  reports need_resched(), we can just move the initial assignment
  down, under the "need_resched_nonpreemptible:" label.

- Try to update the comment after context_switch().

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100519125711.GA30199@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent c676329a

kernel/sched.c

+6 −7
Original line number Diff line number Diff line
@@ -3636,7 +3636,6 @@ asmlinkage void __sched schedule(void) 
	rq = cpu_rq(cpu);

	rcu_note_context_switch(cpu);

	prev = rq->curr;

	switch_count = &prev->nivcsw;



	release_kernel_lock(prev);

need_resched_nonpreemptible:
@@ -3649,6 +3648,7 @@ asmlinkage void __sched schedule(void) 
	raw_spin_lock_irq(&rq->lock);

	clear_tsk_need_resched(prev);



	switch_count = &prev->nivcsw;

	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {

		if (unlikely(signal_pending_state(prev->state, prev))) {

			prev->state = TASK_RUNNING;
@@ -3689,8 +3689,10 @@ asmlinkage void __sched schedule(void) 


		context_switch(rq, prev, next); /* unlocks the rq */

		/*

		 * the context switch might have flipped the stack from under

		 * us, hence refresh the local variables.

		 * The context switch have flipped the stack from under us

		 * and restored the local variables which were saved when

		 * this task called schedule() in the past. prev == current

		 * is still correct, but it can be moved to another cpu/rq.

		 */

		cpu = smp_processor_id();

		rq = cpu_rq(cpu);
@@ -3699,11 +3701,8 @@ asmlinkage void __sched schedule(void) 


	post_schedule(rq);



	if (unlikely(reacquire_kernel_lock(current) < 0)) {

		prev = rq->curr;

		switch_count = &prev->nivcsw;

	if (unlikely(reacquire_kernel_lock(prev)))

		goto need_resched_nonpreemptible;

	}



	preempt_enable_no_resched();

	if (need_resched())