Re: [PATCH] tracing: Fix lockdep warning in global_clock()

Steven Rostedt
2009-12-21T15:49:56Z

On Mon, 2009-12-21 at 07:43 +0100, Ingo Molnar wrote:
> * Li Zefan <lizf@cn.fujitsu.com> wrote:
>
> > # echo 1 > events/enable
> > # echo global > trace_clock
> >
> > ------------[ cut here ]------------
> > WARNING: at kernel/lockdep.c:3162 check_flags+0xb2/0x190()
> > ...
> > ---[ end trace 3f86734a89416623 ]---
> > possible reason: unannotated irqs-on.
> > ...
> >
> > Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> > ---
> > kernel/trace/trace_clock.c | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
> > index 84a3a7b..11563c9 100644
> > --- a/kernel/trace/trace_clock.c
> > +++ b/kernel/trace/trace_clock.c
> > @@ -83,7 +83,7 @@ u64 notrace trace_clock_global(void)
> > int this_cpu;
> > u64 now;
> >
> > - raw_local_irq_save(flags);
> > + local_irq_save(flags);
>
> Hm, wont this cause problems when we trace inside lockdep? Have you tried the
> lockdep events - do they still work?

Doesn't the lockdep code protect against this type of recursion.

Working with interrupts and spin locks in the latency code, I found that
I had to remove all the raw_local_irq_save for the normal
local_irq_save. Because if you disable interrupts with raw_* and then
anything that is called must also disable with raw_*, if they don't then
lockdep will blow up.

-- Steve