linux-kernel - [RFC PATCH 08/11] sched: Fixup task CPUs for potential proxies.

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Date:   Mon,  3 Oct 2022 21:44:58 +0000
From:   "Connor O'Brien" <connoro@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com, John Stultz <jstultz@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Qais Yousef <qais.yousef@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        "Connor O'Brien" <connoro@...gle.com>
Subject: [RFC PATCH 08/11] sched: Fixup task CPUs for potential proxies.

From: Juri Lelli <juri.lelli@...hat.com>

When a mutex owner with potential proxies wakes up those proxies are
activated as well, on the same CPU of the owner. They might have been
sleeping on a different CPU however.

Fixup potential proxies CPU at wakeup time before activating them (or
they get woken up with a wrong CPU reference).

XXX connoro: plan is to fold this into "sched: Add proxy execution" in
future versions.

Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
[Fixed trivial rebase conflict]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
[fix conflicts]
Signed-off-by: Connor O'Brien <connoro@...gle.com>
---
 kernel/sched/core.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 416e61182c17..ad2e7b49f98e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3733,8 +3733,15 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
 			raw_spin_unlock(&pp->blocked_lock);
 			break;
 		}
+		/* XXX can't call set_task_cpu() because we are not holding
+		 * neither pp->pi_lock nor task's rq lock. This should however
+		 * be fine as this task can't be woken up as it is blocked on
+		 * this mutex atm.
+		 * A problem however might be that __set_task_cpu() calls
+		 * set_task_rq() which deals with groups and such...
+		 */
+		__set_task_cpu(pp, cpu_of(rq));
 		activate_task(rq, pp, en_flags);
-		pp->on_rq = TASK_ON_RQ_QUEUED;
 		resched_curr(rq);
 		raw_spin_unlock(&pp->blocked_lock);
 	}
@@ -7114,7 +7121,8 @@ static inline void sched_submit_work(struct task_struct *tsk)
 	 * If a worker goes to sleep, notify and ask workqueue whether it
 	 * wants to wake up a task to maintain concurrency.
 	 */
-	if (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
+	if ((task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) &&
+	    !task_is_blocked(tsk)) {
 		if (task_flags & PF_WQ_WORKER)
 			wq_worker_sleeping(tsk);
 		else
-- 
2.38.0.rc1.362.ged0d419d3c-goog