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sched: Simplify migration_cpu_stop() 

Since, when ->stop_pending, only the stopper can uninstall
p->migration_pending. This could simplify a few ifs, because:

  (pending != NULL) => (pending == p->migration_pending)

Also, the fatty comment above affine_move_task() probably needs a bit
of gardening.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Valentin Schneider 2021-02-25 10:22:30 +01:00 committed by Ingo Molnar
parent ce29ddc47b
commit e140749c9f
1 changed files with 18 additions and 9 deletions
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27
kernel/sched/core.c
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@ -1926,6 +1926,12 @@ static int migration_cpu_stop(void *data)
raw_spin_lock(&p->pi_lock);
rq_lock(rq, &rf);
/*
* If we were passed a pending, then ->stop_pending was set, thus
* p->migration_pending must have remained stable.
*/
WARN_ON_ONCE(pending && pending != p->migration_pending);
/*
* If task_rq(p) != rq, it cannot be migrated here, because we're
* holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
@ -1936,8 +1942,7 @@ static int migration_cpu_stop(void *data)
goto out;
if (pending) {
if (p->migration_pending == pending)
p->migration_pending = NULL;
p->migration_pending = NULL;
complete = true;
}
@ -1976,8 +1981,7 @@ static int migration_cpu_stop(void *data)
* somewhere allowed, we're done.
*/
if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {
if (p->migration_pending == pending)
p->migration_pending = NULL;
p->migration_pending = NULL;
complete = true;
goto out;
}
@ -2165,16 +2169,21 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
*
* (1) In the cases covered above. There is one more where the completion is
* signaled within affine_move_task() itself: when a subsequent affinity request
* cancels the need for an active migration. Consider:
* occurs after the stopper bailed out due to the targeted task still being
* Migrate-Disable. Consider:
*
* Initial conditions: P0->cpus_mask = [0, 1]
*
* P0@CPU0 P1 P2
*
* migrate_disable();
* <preempted>
* CPU0 P1 P2
* <P0>
* migrate_disable();
* <preempted>
* set_cpus_allowed_ptr(P0, [1]);
* <blocks>
* <migration/0>
* migration_cpu_stop()
* is_migration_disabled()
* <bails>
* set_cpus_allowed_ptr(P0, [0, 1]);
* <signal completion>
* <awakes>