From: Kuba Piecuch <jpiecuch@google.com>
To: Kuba Piecuch <jpiecuch@google.com>,
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>,
K Prateek Nayak <kprateek.nayak@amd.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>,
Tejun Heo <tj@kernel.org>, David Vernet <void@manifault.com>,
Andrea Righi <arighi@nvidia.com>,
Changwoo Min <changwoo@igalia.com>, <sched-ext@lists.linux.dev>,
<kernel-team@android.com>
Subject: Re: [RFC][PATCH] sched/ext: Avoid null ptr traversal when ->put_prev_task() is called with NULL next
Date: Mon, 08 Dec 2025 11:15:14 +0000 [thread overview]
Message-ID: <DESSIU61C2DE.1R156AQCNP80C@google.com> (raw)
In-Reply-To: <DESR4ZKLE36H.3MT2T8V3VLV7U@google.com>
On Mon Dec 8, 2025 at 10:10 AM UTC, Kuba Piecuch wrote:
> It looks like it's impossible for an outside observer holding a CPU's rq lock
> to observe a task that is running on that CPU and isn't queued, i.e.
> 'running' implies 'queued' (I'm new to the scheduler so I may be wrong here).
A task that blocks in __schedule() can drop the rq lock while picking the next
task, which is after try_to_block_task() dequeues prev. So it's very much
possible for a task on another CPU to grab the rq lock and observe prev as
dequeued but still running.
next prev parent reply other threads:[~2025-12-08 11:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-06 2:22 [RFC][PATCH] sched/ext: Avoid null ptr traversal when ->put_prev_task() is called with NULL next John Stultz
2025-12-07 13:54 ` Andrea Righi
2025-12-08 10:10 ` Kuba Piecuch
2025-12-08 11:15 ` Kuba Piecuch [this message]
2025-12-08 14:27 ` Kuba Piecuch
2025-12-08 18:23 ` Tejun Heo
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