[tip:,sched/core] sched: Simplify migration_cpu_stop()
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Message ID 161503094413.398.12671142306360940289.tip-bot2@tip-bot2
State New, archived
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  • [tip:,sched/core] sched: Simplify migration_cpu_stop()
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Commit Message

tip-bot2 for Michal Suchanek March 6, 2021, 11:42 a.m. UTC
The following commit has been merged into the sched/core branch of tip:

Commit-ID:     e140749c9f194d65f5984a5941e46758377c93c0
Gitweb:        https://git.kernel.org/tip/e140749c9f194d65f5984a5941e46758377c93c0
Author:        Valentin Schneider <valentin.schneider@arm.com>
AuthorDate:    Thu, 25 Feb 2021 10:22:30 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sat, 06 Mar 2021 12:40:21 +01:00

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>
---
 kernel/sched/core.c | 27 ++++++++++++++++++---------
 1 file changed, 18 insertions(+), 9 deletions(-)

Patch
diff mbox series

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9819121..f9dfb34 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1927,6 +1927,12 @@  static int migration_cpu_stop(void *data)
 	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
 	 * we're holding p->pi_lock.
@@ -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>