linux-kernel - Re: RCU stall on 6.1-rc4 (and some previous releases) related to ftrace

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Date:   Thu, 10 Nov 2022 19:37:12 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "rcu@...r.kernel.org" <rcu@...r.kernel.org>,
        "kernel-dev@...lia.com" <kernel-dev@...lia.com>,
        "Guilherme G. Piccoli" <kernel@...ccoli.net>
Subject: Re: RCU stall on 6.1-rc4 (and some previous releases) related to
 ftrace

On Thu, Nov 10, 2022 at 07:16:51PM -0500, Steven Rostedt wrote:
> On Thu, 10 Nov 2022 18:25:41 -0300
> "Guilherme G. Piccoli" <gpiccoli@...lia.com> wrote:
> 
> > @@ -4184,6 +4184,7 @@ match_records(struct ftrace_hash *hash, char *func, int len, char *mod)
> >  		if (rec->flags & FTRACE_FL_DISABLED)
> >  			continue;
> >  
> > +		cond_resched();
> >  		if (ftrace_match_record(rec, &func_g, mod_match, exclude_mod)) {
> >  			ret = enter_record(hash, rec, clear_filter);
> >  			if (ret < 0) {
> 
> This isn't where I would put it. I would add it after the if statement.
> That is, at the end of the loop.

I am good either way.  Though one could argue for putting it at the
beginning of the loop in case every element takes that "continue" above...

							Thanx, Paul