[PATCH v30 3/7] sched/core: Don't proxy-exec unmatched cookie lock owners

[John Stultz]

From: Vasily Gorbik <gor@xxxxxxxxxxxxx>

Core scheduling chooses a core-wide cookie before __schedule()
installs the next task. With proxy-exec enabled, that task becomes the
donor/scheduling context, and find_proxy_task() may then replace the
execution context with the runnable mutex owner. If its cookie differs
from the selected core cookie, running it would bypass core scheduling's
cookie selection.

When the final mutex owner found by find_proxy_task() does not match the
selected core cookie, stop proxying the donor. If the current execution
context is already in the blocked chain, fall back to idle like the
existing proxy-exec retry paths do. Otherwise deactivate the donor and
let __schedule() pick again. The mutex owner can be picked later under
its own cookie.

Fixes: 7de9d4f94638 ("sched: Start blocked_on chain processing in find_proxy_task()")
Reported-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Link: https://lore.kernel.org/lkml/10282ce9-f4ae-498f-9b57-f4e1e61fffbc@xxxxxxx/
Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
[jstultz: Added tweak to ensure we deactivate donor, not runnable owner]
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
---
Cc: Joel Fernandes <joelagnelf@xxxxxxxxxx>
Cc: Qais Yousef <qyousef@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Zimuzo Ezeozue <zezeozue@xxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Metin Kaya <Metin.Kaya@xxxxxxx>
Cc: Xuewen Yan <xuewen.yan94@xxxxxxxxx>
Cc: K Prateek Nayak <kprateek.nayak@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: Suleiman Souhlal <suleiman@xxxxxxxxxx>
Cc: kuyo chang <kuyo.chang@xxxxxxxxxxxx>
Cc: hupu <hupu.gm@xxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
---
 kernel/sched/core.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8e661b5f133d7..36e1db67a8374 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7004,6 +7004,14 @@ find_proxy_task(struct rq *rq, struct task_struct *donor, struct rq_flags *rf)
 		owner->blocked_donor = p;
 	}
 	WARN_ON_ONCE(owner && !owner->on_rq);
+
+	if (owner && !sched_cpu_cookie_match(rq, owner)) {
+		if (curr_in_chain)
+			return proxy_resched_idle(rq);
+		p = donor; /* Deactivate the donor, not the runnable owner */
+		clear_task_blocked_on(p, NULL);
+		goto deactivate;
+	}
 	return owner;
 
 deactivate:
-- 
2.55.0.rc0.799.gd6f94ed593-goog