linux-kernel - Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all

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Date:   Thu, 6 Dec 2018 10:59:14 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Will Deacon <will.deacon@....com>
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        keescook@...omium.org, arnd@...db.de,
        linux-arm-kernel@...ts.infradead.org,
        Anders Roxell <anders.roxell@...aro.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before
 ftrace_modify_all_code()

On Thu, 6 Dec 2018 13:20:07 +0000
Will Deacon <will.deacon@....com> wrote:

> On Wed, Dec 05, 2018 at 12:48:54PM -0500, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> > 
> > It has been reported that ftrace_replace_code() which is called by
> > ftrace_modify_all_code() can cause a soft lockup warning for an
> > allmodconfig kernel. This is because all the debug options enabled
> > causes the loop in ftrace_replace_code() (which loops over all the
> > functions being enabled where there can be 10s of thousands), is too
> > slow, and never schedules out.
> > 
> > To solve this, setting FTRACE_SCHEDULABLE to the command passed into
> > ftrace_replace_code() will make it call cond_resched() in the loop,
> > which prevents the soft lockup warning from triggering.
> > 
> > Link: http://lkml.kernel.org/r/20181204192903.8193-1-anders.roxell@linaro.org
> > 
> > Reported-by: Anders Roxell <anders.roxell@...aro.org>
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > ---
> >  arch/arm64/kernel/ftrace.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> > index 57e962290df3..9a8de0a79f97 100644
> > --- a/arch/arm64/kernel/ftrace.c
> > +++ b/arch/arm64/kernel/ftrace.c
> > @@ -193,6 +193,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
> >  
> >  void arch_ftrace_update_code(int command)
> >  {
> > +	command |= FTRACE_SCHEDULABLE;
> >  	ftrace_modify_all_code(command);
> >  }  
> 
> Bikeshed: I'd probably go for FTRACE_MAY_SLEEP, but I'm not going to die
> on that hill so...

I like bike sheds. Hmm, it's not too late to change this. Perhaps I
will.

> 
> Acked-by: Will Deacon <will.deacon@....com>

Thanks!

If I decide to change the name to MAY_SLEEP, I assume I can still keep
your Acked-by.

-- Steve