linux-kernel - Re: [PATCH 3/3] arm64: ftrace: add cond_resched() to func ftrace_make

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Date:   Tue, 4 Dec 2018 12:26:27 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Anders Roxell <anders.roxell@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] arm64: ftrace: add cond_resched() to func
 ftrace_make_(call|nop)

On Tue, 4 Dec 2018 11:12:43 +0000
Will Deacon <will.deacon@....com> wrote:

> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 8ef9fc226037..42e89397778b 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -2393,11 +2393,14 @@ void __weak ftrace_replace_code(int enable)
> >  {
> >  	struct dyn_ftrace *rec;
> >  	struct ftrace_page *pg;
> > +	bool schedulable;
> >  	int failed;
> >  
> >  	if (unlikely(ftrace_disabled))
> >  		return;
> >  
> > +	schedulable = !irqs_disabled() & !preempt_count();  
> 
> Looks suspiciously like a bitwise preemptible() to me!

Ah, thanks. Yeah, that should have been &&. But what did you expect.
I didn't even compile this ;-)

> 
> > +
> >  	do_for_each_ftrace_rec(pg, rec) {
> >  
> >  		if (rec->flags & FTRACE_FL_DISABLED)
> > @@ -2409,6 +2412,8 @@ void __weak ftrace_replace_code(int enable)
> >  			/* Stop processing */
> >  			return;
> >  		}
> > +		if (schedulable)
> > +			cond_resched();
> >  	} while_for_each_ftrace_rec();
> >  }  
> 
> If this solves the problem in core code, them I'm all for it. Otherwise, I
> was thinking of rolling our own ftrace_replace_code() for arm64, but that's
> going to involve a fair amount of duplication.
> 

If it does, then I'll add it. Or take a patch for it ;-) 

My main concern is that this can be called from non schedulable context.

-- Steve