linux-kernel - Re: [RFC][PATCH] sched,livepatch: Untangle cond

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Message-ID: <alpine.LSU.2.21.2503261552360.4152@pobox.suse.cz>
Date: Wed, 26 Mar 2025 15:54:48 +0100 (CET)
From: Miroslav Benes <mbenes@...e.cz>
To: Peter Zijlstra <peterz@...radead.org>
cc: Josh Poimboeuf <jpoimboe@...hat.com>, mingo@...nel.com, 
    juri.lelli@...hat.com, vincent.guittot@...aro.org, 
    dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
    mgorman@...e.de, vschneid@...hat.com, jpoimboe@...nel.org, 
    jikos@...nel.org, pmladek@...e.com, joe.lawrence@...hat.com, 
    linux-kernel@...r.kernel.org, live-patching@...r.kernel.org, 
    Thomas Gleixner <tglx@...utronix.de>, 
    Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [RFC][PATCH] sched,livepatch: Untangle cond_resched() and
 live-patching

>  void __klp_sched_try_switch(void)
>  {
> -	if (likely(!klp_patch_pending(current)))
> -		return;
> -
>  	/*
>  	 * This function is called from cond_resched() which is called in many
>  	 * places throughout the kernel.  Using the klp_mutex here might
> @@ -377,14 +365,14 @@ void __klp_sched_try_switch(void)
>  	 * klp_try_switch_task().  Thanks to task_call_func() they won't be
>  	 * able to switch this task while it's running.
>  	 */
> -	preempt_disable();
> +	lockdep_assert_preemption_disabled();
>  
>  	/*
>  	 * Make sure current didn't get patched between the above check and
>  	 * preempt_disable().
>  	 */
>  	if (unlikely(!klp_patch_pending(current)))
> -		goto out;
> +		return;

It does not look correct. We just make sure that 
klp_patch_pending(current) did not change here. It would be highly 
unlikely. However, we should keep the likely way out (the first removed 
condition above). So let's also s/unlikely/likely/ here.

And the comments in the function should be updated as well.

Miroslav