linux-kernel - Re: [PATCH] percpu: make this_cpu_generic

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Date:   Fri, 16 Sep 2016 10:53:09 +0100
From:   Will Deacon <will.deacon@....com>
To:     Chunyan Zhang <zhang.chunyan@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-arch@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Lyra Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH] percpu: make this_cpu_generic_read notrace

On Fri, Sep 16, 2016 at 04:42:44PM +0800, Chunyan Zhang wrote:
> Hi Will and Steven,
> 
> May I have a review or an acked-by from you on this patch so that Arnd
> can pick it up.
> 
> I have tested this patch on arm qemu, I'm sure it can solve the
> problem described in commit message.

It looks fine to me; we took your equivalent patch for arm64 already, so:

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

Will

> On 10 September 2016 at 16:45, Chunyan Zhang <zhang.chunyan@...aro.org> wrote:
> > When debug preempt or preempt tracer is enabled, preempt_count_add/sub()
> > can be traced by function and function graph tracing, and
> > preempt_disable/enable() would call preempt_count_add/sub(), so
> > we should use preempt_disable/enable_notrace in Ftrace subsystem.
> >
> > The function this_cpu_read() started being used by function graph tracing
> > after the commit 345ddcc882d8 ("ftrace: Have set_ftrace_pid use the
> > bitmap like events do"), so it has to use preempt_disable/enable_notrace
> > instead now.
> >
> > Signed-off-by: Chunyan Zhang <zhang.chunyan@...aro.org>
> > ---
> >  include/asm-generic/percpu.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/asm-generic/percpu.h b/include/asm-generic/percpu.h
> > index 4d9f233..70fefec 100644
> > --- a/include/asm-generic/percpu.h
> > +++ b/include/asm-generic/percpu.h
> > @@ -108,9 +108,9 @@ do {                                                                        \
> >  #define this_cpu_generic_read(pcp)                                     \
> >  ({                                                                     \
> >         typeof(pcp) __ret;                                              \
> > -       preempt_disable();                                              \
> > +       preempt_disable_notrace();                                      \
> >         __ret = *this_cpu_ptr(&(pcp));                                  \
> > -       preempt_enable();                                               \
> > +       preempt_enable_notrace();                                       \
> >         __ret;                                                          \
> >  })
> >
> > --
> > 2.7.4
> >
>