[PATCH RT 24/32] sched: migrate_enable: Use stop_one_cpu_nowait()

Steven Rostedt
2020-01-17T17:41:44Z

From: Scott Wood <swood@redhat.com>

[ Upstream commit 6b39a1fa8c53cae08dc03afdae193b7d3a78a173 ]

migrate_enable() can be called with current->state != TASK_RUNNING.
Avoid clobbering the existing state by using stop_one_cpu_nowait().
Since we're stopping the current cpu, we know that we won't get
past __schedule() until migration_cpu_stop() has run (at least up to
the point of migrating us to another cpu).

Signed-off-by: Scott Wood <swood@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
include/linux/stop_machine.h | 2 ++
kernel/sched/core.c | 23 +++++++++++++----------
kernel/stop_machine.c | 7 +++++--
3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/include/linux/stop_machine.h b/include/linux/stop_machine.h
index 6d3635c86dbe..82fc686ddd9e 100644
--- a/include/linux/stop_machine.h
+++ b/include/linux/stop_machine.h
@@ -26,6 +26,8 @@ struct cpu_stop_work {
cpu_stop_fn_t fn;
void *arg;
struct cpu_stop_done *done;
+ /* Did not run due to disabled stopper; for nowait debug checks */
+ bool disabled;
};

int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e97ac751aad2..e465381b464d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -990,6 +990,7 @@ static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
struct migration_arg {
struct task_struct *task;
int dest_cpu;
+ bool done;
};

/*
@@ -1025,6 +1026,11 @@ static int migration_cpu_stop(void *data)
struct task_struct *p = arg->task;
struct rq *rq = this_rq();
struct rq_flags rf;
+ int dest_cpu = arg->dest_cpu;
+
+ /* We don't look at arg after this point. */
+ smp_mb();
+ arg->done = true;

/*
* The original target CPU might have gone down and we might
@@ -1047,9 +1053,9 @@ static int migration_cpu_stop(void *data)
*/
if (task_rq(p) == rq) {
if (task_on_rq_queued(p))
- rq = __migrate_task(rq, &rf, p, arg->dest_cpu);
+ rq = __migrate_task(rq, &rf, p, dest_cpu);
else
- p->wake_cpu = arg->dest_cpu;
+ p->wake_cpu = dest_cpu;
}
rq_unlock(rq, &rf);
raw_spin_unlock(&p->pi_lock);
@@ -7322,6 +7328,7 @@ void migrate_enable(void)
WARN_ON(smp_processor_id() != cpu);
if (!is_cpu_allowed(p, cpu)) {
struct migration_arg arg = { p };
+ struct cpu_stop_work work;
struct rq_flags rf;

rq = task_rq_lock(p, &rf);
@@ -7329,15 +7336,11 @@ void migrate_enable(void)
arg.dest_cpu = select_fallback_rq(cpu, p);
task_rq_unlock(rq, p, &rf);

- preempt_lazy_enable();
- preempt_enable();
-
- sleeping_lock_inc();
- stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
- sleeping_lock_dec();
+ stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop,
+ &arg, &work);
tlb_migrate_finish(p->mm);
-
- return;
+ __schedule(true);
+ WARN_ON_ONCE(!arg.done && !work.disabled);
}

out:
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 067cb83f37ea..2d15c0d50625 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -86,8 +86,11 @@ static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
enabled = stopper->enabled;
if (enabled)
__cpu_stop_queue_work(stopper, work, &wakeq);
- else if (work->done)
- cpu_stop_signal_done(work->done);
+ else {
+ work->disabled = true;
+ if (work->done)
+ cpu_stop_signal_done(work->done);
+ }
raw_spin_unlock_irqrestore(&stopper->lock, flags);

wake_up_q(&wakeq);
--
2.24.1