Commit 9e81889c authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Fix affine_move_task() self-concurrency 



Consider:

   sched_setaffinity(p, X);		sched_setaffinity(p, Y);

Then the first will install p->migration_pending = &my_pending; and
issue stop_one_cpu_nowait(pending); and the second one will read
p->migration_pending and _also_ issue: stop_one_cpu_nowait(pending),
the _SAME_ @pending.

This causes stopper list corruption.

Add set_affinity_pending::stop_pending, to indicate if a stopper is in
progress.

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/20210224131355.649146419@infradead.org
parent 3f1bc119

kernel/sched/core.c

+12 −3
Original line number Diff line number Diff line
@@ -1864,6 +1864,7 @@ struct migration_arg { 


struct set_affinity_pending {

	refcount_t		refs;

	unsigned int		stop_pending;

	struct completion	done;

	struct cpu_stop_work	stop_work;

	struct migration_arg	arg;
@@ -1982,12 +1983,15 @@ static int migration_cpu_stop(void *data) 
		 * determine is_migration_disabled() and so have to chase after

		 * it.

		 */

		WARN_ON_ONCE(!pending->stop_pending);

		task_rq_unlock(rq, p, &rf);

		stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,

				    &pending->arg, &pending->stop_work);

		return 0;

	}

out:

	if (pending)

		pending->stop_pending = false;

	task_rq_unlock(rq, p, &rf);



	if (complete)
@@ -2183,7 +2187,7 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
			    int dest_cpu, unsigned int flags)

{

	struct set_affinity_pending my_pending = { }, *pending = NULL;

	bool complete = false;

	bool stop_pending, complete = false;



	/* Can the task run on the task's current CPU? If so, we're done */

	if (cpumask_test_cpu(task_cpu(p), &p->cpus_mask)) {
@@ -2256,14 +2260,19 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag 
		 * anything else we cannot do is_migration_disabled(), punt

		 * and have the stopper function handle it all race-free.

		 */

		stop_pending = pending->stop_pending;

		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) {

			stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop,

					    &pending->arg, &pending->stop_work);

		}



		if (flags & SCA_MIGRATE_ENABLE)

			return 0;