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 v27 02/10] sched: Avoid donor->sched_class->yield_task() null traversal
Date: Sat, 4 Apr 2026 11:27:50 +0530 [thread overview]
Message-ID: <1ae3d7ea-415a-4e60-a94b-6b817b4c8561@amd.com> (raw)
In-Reply-To: <20260404053632.1729280-3-jstultz@google.com>
Hello John,
On 4/4/2026 11:06 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.
After introduction of proxy_resched_idle(), we shouldn't
have any case of running with rq->idle as donor with a
different rq->curr.
I think we can drop this fix now and squash the changes from
Patch 7 into Patch 6 to even avoid any transient cases during
bisection where this might be possible
Thoughts?
--
Thanks and Regards,
Prateek
next prev parent reply other threads:[~2026-04-04 5:58 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-04 5:36 [PATCH v27 00/10] Optimized Donor Migration for Proxy Execution John Stultz
2026-04-04 5:36 ` [PATCH v27 01/10] sched: Rework pick_next_task() and prev_balance() to avoid stale prev references John Stultz
2026-04-04 5:36 ` [PATCH v27 02/10] sched: Avoid donor->sched_class->yield_task() null traversal John Stultz
2026-04-04 5:57 ` K Prateek Nayak [this message]
2026-04-04 6:09 ` John Stultz
2026-04-04 5:36 ` [PATCH v27 03/10] sched: deadline: Add some helper variables to cleanup deadline logic John Stultz
2026-04-04 5:36 ` [PATCH v27 04/10] sched: deadline: Add dl_rq->curr pointer to address issues with Proxy Exec John Stultz
2026-04-04 5:36 ` [PATCH v27 05/10] sched: Rework block_task so it can be directly called John Stultz
2026-04-04 5:36 ` [PATCH v27 06/10] sched: Have try_to_wake_up() handle return-migration for PROXY_WAKING case John Stultz
2026-04-04 5:36 ` [PATCH v27 07/10] sched/core: Reset the donor to current task when donor is woken John Stultz
2026-04-04 5:36 ` [PATCH v27 08/10] sched: Add blocked_donor link to task for smarter mutex handoffs John Stultz
2026-04-04 5:36 ` [PATCH v27 09/10] sched: Break out core of attach_tasks() helper into sched.h John Stultz
2026-04-04 5:36 ` [PATCH v27 10/10] sched: Migrate whole chain in proxy_migrate_task() John Stultz
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