Re: [PATCH 2/2] arm64: ftrace: Set FTRACE_SCHEDULABLE before ftrace_modify_all_code()

[Anders Roxell]

On Thu, 6 Dec 2018 at 14:19, Will Deacon <will.deacon@xxxxxxx> wrote:
>
> On Wed, Dec 05, 2018 at 12:48:54PM -0500, Steven Rostedt wrote:
> > From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
> >
> > 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@xxxxxxxxxx
> >
> > Reported-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
> > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> > ---
> >  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...
>
> Acked-by: Will Deacon <will.deacon@xxxxxxx>

Tested-by: Anders Roxell <anders.roxell@xxxxxxxxxx>

Cheers,
Anders

>
> Thanks, Steve!
>
> Will