linux-kernel - Re: [x86, build] 6dafca9780: WARNING:at_arch/x86/kernel/ftrace.c:#ftrace_verify

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Message-ID: <CABCJKufOTubpoJyWQ5aMzgeiNsTRuO61T5FMEG=jFwnO0XZ-pQ@mail.gmail.com>
Date:   Mon, 1 Mar 2021 19:23:03 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     kernel test robot <oliver.sang@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        kernel test robot <lkp@...el.com>
Subject: Re: [x86, build] 6dafca9780: WARNING:at_arch/x86/kernel/ftrace.c:#ftrace_verify_code

On Mon, Mar 1, 2021 at 6:47 PM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Mon, 1 Mar 2021 18:40:32 -0800
> Sami Tolvanen <samitolvanen@...gle.com> wrote:
>
> > On Mon, Mar 01, 2021 at 08:15:26PM -0500, Steven Rostedt wrote:
> > > On Mon, 1 Mar 2021 16:03:51 -0800
> > > Sami Tolvanen <samitolvanen@...gle.com> wrote:
> > > >
> > > > >                 ret = ftrace_verify_code(rec->ip, old);
> > > > > +
> > > > > +               if (__is_defined(CC_USING_NOP_MCOUNT) && ret && old_nop) {
> > > > > +                       /* Compiler could have put in P6_NOP5 */
> > > > > +                       old = P6_NOP5;
> > > > > +                       ret = ftrace_verify_code(rec->ip, old);
> > > > > +               }
> > > > > +
> > > >
> > > > Wouldn't that still hit WARN(1) in the initial ftrace_verify_code()
> > > > call if ideal_nops doesn't match?
> > >
> > > That was too quickly written ;-)
> > >
> > > Take 2:
> > >
> > > [ with fixes for setting p6_nop ]
> >
> > Thanks, I tested this with the config from the build bot, and I can
> > confirm that it fixes the issue for me.
> >
> > I also tested a quick patch to disable the __fentry__ conversion in
> > objtool, and it seems to work too, but it's probably a good idea to
> > fix the issue with CC_USING_NOP_MCOUNT in any case.
>
> Thanks for testing, I'll make this into a proper patch and start
> testing it internally. I'm assuming you want this to go into the -rc
> release and possibly stable?

Sounds good, thank you. Yes, getting the fix to -rc would be great.
I'm not sure if it's necessary in -stable though, the objtool patch is
only in -rc1.

Sami