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

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Date:   Tue, 4 Dec 2018 19:07:16 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     rostedt@...dmis.org
Cc:     Will Deacon <will.deacon@....com>, Arnd Bergmann <arnd@...db.de>,
        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 at 18:26, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> 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 ;-)

I tested your patch. it worked.

I'll send a patch shortly.

Cheers,
Anders