linux-kernel - Re: [PATCH v3 12/17] sched: Adapt sched tracepoints for RV task model

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250716123832.GW1613200@noisy.programming.kicks-ass.net>
Date: Wed, 16 Jul 2025 14:38:32 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-trace-kernel@...r.kernel.org, Nam Cao <namcao@...utronix.de>,
	Tomas Glozar <tglozar@...hat.com>, Juri Lelli <jlelli@...hat.com>,
	Clark Williams <williams@...hat.com>,
	John Kacur <jkacur@...hat.com>
Subject: Re: [PATCH v3 12/17] sched: Adapt sched tracepoints for RV task model

On Tue, Jul 15, 2025 at 09:14:29AM +0200, Gabriele Monaco wrote:
> Add the following tracepoints:
> * sched_set_need_resched(tsk, cpu, tif)
>     Called when a task is set the need resched [lazy] flag
> * sched_switch_vain(preempt, tsk, tsk_state)
>     Called when a task is selected again during __schedule
>     i.e. prev == next == tsk : no real context switch

> @@ -6592,6 +6598,7 @@ static bool try_to_block_task(struct rq *rq, struct task_struct *p,
>  	int flags = DEQUEUE_NOCLOCK;
>  
>  	if (signal_pending_state(task_state, p)) {
> +		trace_sched_set_state_tp(p, TASK_RUNNING, true);
>  		WRITE_ONCE(p->__state, TASK_RUNNING);
>  		*task_state_p = TASK_RUNNING;
>  		return false;

I'm confused on the purpose of this. How does this relate to say the
wakeup in signal_wake_up_state() ?

> @@ -6786,6 +6793,7 @@ static void __sched notrace __schedule(int sched_mode)
>  		rq = context_switch(rq, prev, next, &rf);
>  	} else {
>  		rq_unpin_lock(rq, &rf);
> +		trace_sched_switch_vain_tp(preempt, prev, prev_state);
>  		__balance_callbacks(rq);
>  		raw_spin_rq_unlock_irq(rq);
>  	}

Hurmph... don't you already have this covered by: trace_sched_exit_tp() ?

Specifically, the only case where is_switch := false, is this case.