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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1v5pjG-0000000H6Cb-0C5Z; Mon, 06 Oct 2025 18:14:34 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 1EAA1300212; Mon, 06 Oct 2025 20:14:29 +0200 (CEST) Date: Mon, 6 Oct 2025 20:14:29 +0200 From: Peter Zijlstra To: Shrikanth Hegde Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, longman@redhat.com, hannes@cmpxchg.org, mkoutny@suse.com, void@manifault.com, arighi@nvidia.com, changwoo@igalia.com, cgroups@vger.kernel.org, sched-ext@lists.linux.dev, liuwenfang@honor.com, tglx@linutronix.de, tj@kernel.org Subject: Re: [PATCH 01/14] sched: Employ sched_change guards Message-ID: <20251006181429.GV3245006@noisy.programming.kicks-ass.net> References: <20250910154409.446470175@infradead.org> <20250910155808.415580225@infradead.org> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Oct 06, 2025 at 08:51:27PM +0530, Shrikanth Hegde wrote: > > > On 9/10/25 9:14 PM, Peter Zijlstra wrote: > > As proposed a long while ago -- and half done by scx -- wrap the > > scheduler's 'change' pattern in a guard helper. > > > [...]> put_task_struct(p); > > --- a/kernel/sched/sched.h > > +++ b/kernel/sched/sched.h > > @@ -3860,23 +3860,22 @@ extern void check_class_changed(struct r > > extern struct balance_callback *splice_balance_callbacks(struct rq *rq); > > extern void balance_callbacks(struct rq *rq, struct balance_callback *head); > > -#ifdef CONFIG_SCHED_CLASS_EXT > > -/* > > - * Used by SCX in the enable/disable paths to move tasks between sched_classes > > - * and establish invariants. > > - */ > > -struct sched_enq_and_set_ctx { > > +struct sched_change_ctx { > > struct task_struct *p; > > - int queue_flags; > > + int flags; > > bool queued; > > bool running; > > }; > > -void sched_deq_and_put_task(struct task_struct *p, int queue_flags, > > - struct sched_enq_and_set_ctx *ctx); > > -void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx); > > +struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int flags); > > +void sched_change_end(struct sched_change_ctx *ctx); > > -#endif /* CONFIG_SCHED_CLASS_EXT */ > > +DEFINE_CLASS(sched_change, struct sched_change_ctx *, > > + sched_change_end(_T), > > + sched_change_begin(p, flags), > > + struct task_struct *p, unsigned int flags) > > + > > +DEFINE_CLASS_IS_UNCONDITIONAL(sched_change) > > #include "ext.h" > could you please add a comment on matching flags on dequeue/enqueue > here? Would something like so be okay? This assumes at least the second patch is applied as well. --- --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10783,6 +10783,12 @@ struct sched_change_ctx *sched_change_be struct sched_change_ctx *ctx = this_cpu_ptr(&sched_change_ctx); struct rq *rq = task_rq(p); + /* + * Must exclusively use matched flags since this is both dequeue and + * enqueue. + */ + WARN_ON_ONCE(flags & 0xFFFF0000); + lockdep_assert_rq_held(rq); if (!(flags & DEQUEUE_NOCLOCK)) {