Commit 50caf9c1 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Simplify set_affinity_pending refcounts 



Now that we have set_affinity_pending::stop_pending to indicate if a
stopper is in progress, and we have the guarantee that if that stopper
exists, it will (eventually) complete our @pending we can simplify the
refcount scheme by no longer counting the stopper thread.

Fixes: 6d337eab ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()")
Cc: stable@kernel.org
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224131355.724130207@infradead.org
parent 9e81889c

kernel/sched/core.c

+20 −12
Original line number Diff line number Diff line
@@ -1862,6 +1862,10 @@ struct migration_arg { 
	struct set_affinity_pending	*pending;

};



/*

 * @refs: number of wait_for_completion()

 * @stop_pending: is @stop_work in use

 */

struct set_affinity_pending {

	refcount_t		refs;

	unsigned int		stop_pending;
@@ -1997,10 +2001,6 @@ static int migration_cpu_stop(void *data) 
	if (complete)

		complete_all(&pending->done);



	/* For pending->{arg,stop_work} */

	if (pending && refcount_dec_and_test(&pending->refs))

		wake_up_var(&pending->refs);



	return 0;

}
@@ -2199,12 +2199,16 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
			push_task = get_task_struct(p);

		}



		/*

		 * If there are pending waiters, but no pending stop_work,

		 * then complete now.

		 */

		pending = p->migration_pending;

		if (pending) {

			refcount_inc(&pending->refs);

		if (pending && !pending->stop_pending) {

			p->migration_pending = NULL;

			complete = true;

		}



		task_rq_unlock(rq, p, rf);



		if (push_task) {
@@ -2213,7 +2217,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
		}



		if (complete)

			goto do_complete;

			complete_all(&pending->done);



		return 0;

	}
@@ -2264,9 +2268,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
		if (!stop_pending)

			pending->stop_pending = true;



		refcount_inc(&pending->refs); /* pending->{arg,stop_work} */

		if (flags & SCA_MIGRATE_ENABLE)

			p->migration_flags &= ~MDF_PUSH;



		task_rq_unlock(rq, p, rf);



		if (!stop_pending) {
@@ -2282,12 +2286,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
			if (task_on_rq_queued(p))

				rq = move_queued_task(rq, rf, p, dest_cpu);



			if (!pending->stop_pending) {

				p->migration_pending = NULL;

				complete = true;

			}

		}

		task_rq_unlock(rq, p, rf);



do_complete:

		if (complete)

			complete_all(&pending->done);

	}
@@ -2295,7 +2300,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
	wait_for_completion(&pending->done);



	if (refcount_dec_and_test(&pending->refs))

		wake_up_var(&pending->refs);

		wake_up_var(&pending->refs); /* No UaF, just an address */



	/*

	 * Block the original owner of &pending until all subsequent callers
@@ -2303,6 +2308,9 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
	 */

	wait_var_event(&my_pending.refs, !refcount_read(&my_pending.refs));



	/* ARGH */

	WARN_ON_ONCE(my_pending.stop_pending);



	return 0;

}