From: K Prateek Nayak <kprateek.nayak@amd.com>
To: John Stultz <jstultz@google.com>, LKML <linux-kernel@vger.kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>,
Qais Yousef <qyousef@layalina.io>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
"Juri Lelli" <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Valentin Schneider <vschneid@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>,
Zimuzo Ezeozue <zezeozue@google.com>,
Mel Gorman <mgorman@suse.de>, Will Deacon <will@kernel.org>,
Waiman Long <longman@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Metin Kaya <Metin.Kaya@arm.com>,
Xuewen Yan <xuewen.yan94@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
"Daniel Lezcano" <daniel.lezcano@linaro.org>,
Suleiman Souhlal <suleiman@google.com>,
kuyo chang <kuyo.chang@mediatek.com>, hupu <hupu.gm@gmail.com>,
<kernel-team@android.com>
Subject: Re: [PATCH v24 08/11] sched: Avoid donor->sched_class->yield_task() null traversal
Date: Tue, 30 Dec 2025 11:31:04 +0530 [thread overview]
Message-ID: <bbe741b6-db02-4c4c-9bd7-b3eeaf3ed486@amd.com> (raw)
In-Reply-To: <20251124223111.3616950-9-jstultz@google.com>
Hello John,
On 11/25/2025 4:01 AM, John Stultz wrote:
> With proxy-exec once we do return migration from ttwu(), if a
> task is proxying for a waiting donor, and the donor is woken up,
> we switch the rq->donor to point to idle briefly until we can
> re-enter __schedule().
>
> However, if a task that was acting as a proxy calls into
> yield() right after the donor is switched to idle, it may
> trip a null pointer traversal, because the idle task doesn't
> have a yield_task() pointer.
I thought that was a transient state that should not be observed by the
running task.
Since NEED_RESCHED is retained, we'll just go though another pass of
__schedule() loop and the task should not observe rq->donor as idle in
do_sched_yield() as only the current task can yield on the local CPU.
Do we have a splat that suggests this happens?
--
Thanks and Regards,
Prateek
next prev parent reply other threads:[~2025-12-30 6:01 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-24 22:30 [PATCH v24 00/11] Donor Migration for Proxy Execution (v24) John Stultz
2025-11-24 22:30 ` [PATCH v24 01/11] locking: Add task::blocked_lock to serialize blocked_on state John Stultz
2025-11-24 22:30 ` [PATCH v24 02/11] sched: Fix modifying donor->blocked on without proper locking John Stultz
2025-11-24 22:30 ` [PATCH v24 03/11] sched/locking: Add special p->blocked_on==PROXY_WAKING value for proxy return-migration John Stultz
2025-11-24 22:30 ` [PATCH v24 04/11] sched: Add assert_balance_callbacks_empty helper John Stultz
2025-11-24 22:30 ` [PATCH v24 05/11] sched: Add logic to zap balance callbacks if we pick again John Stultz
2025-11-24 22:30 ` [PATCH v24 06/11] sched: Handle blocked-waiter migration (and return migration) John Stultz
2025-12-30 5:33 ` K Prateek Nayak
2026-03-07 6:48 ` John Stultz
2026-03-10 4:17 ` K Prateek Nayak
2025-11-24 22:30 ` [PATCH v24 07/11] sched: Rework pick_next_task() and prev_balance() to avoid stale prev references John Stultz
2025-11-24 22:31 ` [PATCH v24 08/11] sched: Avoid donor->sched_class->yield_task() null traversal John Stultz
2025-12-30 6:01 ` K Prateek Nayak [this message]
2025-12-30 9:52 ` K Prateek Nayak
2026-01-01 7:04 ` K Prateek Nayak
2025-11-24 22:31 ` [PATCH v24 09/11] sched: Have try_to_wake_up() handle return-migration for PROXY_WAKING case John Stultz
2026-01-01 9:53 ` K Prateek Nayak
2026-03-11 6:45 ` John Stultz
2026-03-11 9:25 ` K Prateek Nayak
2025-11-24 22:31 ` [PATCH v24 10/11] sched: Add blocked_donor link to task for smarter mutex handoffs John Stultz
2025-11-24 22:31 ` [PATCH v24 11/11] sched: Migrate whole chain in proxy_migrate_task() John Stultz
2025-12-30 6:46 ` K Prateek Nayak
2026-03-07 7:07 ` John Stultz
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