From: Greg Kroah-Hartman gregkh@linuxfoundation.org
From: Peter Zijlstra peterz@infradead.org
commit c20cf065d4a619d394d23290093b1002e27dff86 upstream.
When affine_move_task() issues a migration_cpu_stop(), the purpose of that function is to complete that @pending, not any random other p->migration_pending that might have gotten installed since.
This realization much simplifies migration_cpu_stop() and allows further necessary steps to fix all this as it provides the guarantee that @pending's stopper will complete @pending (and not some random other @pending).
Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") Cc: stable@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Valentin Schneider valentin.schneider@arm.com Link: https://lkml.kernel.org/r/20210224131355.430014682@infradead.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/core.c | 56 +++++++--------------------------------------------- 1 file changed, 8 insertions(+), 48 deletions(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1898,8 +1898,8 @@ static struct rq *__migrate_task(struct */ static int migration_cpu_stop(void *data) { - struct set_affinity_pending *pending; struct migration_arg *arg = data; + struct set_affinity_pending *pending = arg->pending; struct task_struct *p = arg->task; int dest_cpu = arg->dest_cpu; struct rq *rq = this_rq(); @@ -1921,25 +1921,6 @@ static int migration_cpu_stop(void *data raw_spin_lock(&p->pi_lock); rq_lock(rq, &rf);
- pending = p->migration_pending; - if (pending && !arg->pending) { - /* - * This happens from sched_exec() and migrate_task_to(), - * neither of them care about pending and just want a task to - * maybe move about. - * - * Even if there is a pending, we can ignore it, since - * affine_move_task() will have it's own stop_work's in flight - * which will manage the completion. - * - * Notably, pending doesn't need to match arg->pending. This can - * happen when tripple concurrent affine_move_task() first sets - * pending, then clears pending and eventually sets another - * pending. - */ - pending = NULL; - } - /* * 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 @@ -1950,31 +1931,20 @@ static int migration_cpu_stop(void *data goto out;
if (pending) { - p->migration_pending = NULL; + if (p->migration_pending == pending) + p->migration_pending = NULL; complete = true; }
- /* migrate_enable() -- we must not race against SCA */ - if (dest_cpu < 0) { - /* - * When this was migrate_enable() but we no longer - * have a @pending, a concurrent SCA 'fixed' things - * and we should be valid again. Nothing to do. - */ - if (!pending) { - WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)); - goto out; - } - + if (dest_cpu < 0) dest_cpu = cpumask_any_distribute(&p->cpus_mask); - }
if (task_on_rq_queued(p)) rq = __migrate_task(rq, &rf, p, dest_cpu); else p->wake_cpu = dest_cpu;
- } else if (dest_cpu < 0 || pending) { + } else if (pending) { /* * This happens when we get migrated between migrate_enable()'s * preempt_enable() and scheduling the stopper task. At that @@ -1989,23 +1959,14 @@ static int migration_cpu_stop(void *data * ->pi_lock, so the allowed mask is stable - if it got * somewhere allowed, we're done. */ - if (pending && cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) { - p->migration_pending = NULL; + if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) { + if (p->migration_pending == pending) + p->migration_pending = NULL; complete = true; goto out; }
/* - * When this was migrate_enable() but we no longer have an - * @pending, a concurrent SCA 'fixed' things and we should be - * valid again. Nothing to do. - */ - if (!pending) { - WARN_ON_ONCE(!cpumask_test_cpu(task_cpu(p), &p->cpus_mask)); - goto out; - } - - /* * When migrate_enable() hits a rq mis-match we can't reliably * determine is_migration_disabled() and so have to chase after * it. @@ -2022,7 +1983,6 @@ out: complete_all(&pending->done);
/* For pending->{arg,stop_work} */ - pending = arg->pending; if (pending && refcount_dec_and_test(&pending->refs)) wake_up_var(&pending->refs);