Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

Steven Rostedt
2009-02-23T15:42:18Z

On Mon, 23 Feb 2009, Steven Rostedt wrote:

>
>
> On Sun, 22 Feb 2009, Frederic Weisbecker wrote:
>
> > Impact: fix unwaken pipe
> >
> > Now that we use a common wakeup infrastructure, we must append a wakeup
> > on few callsites which lack it or tasks reading trace_pipe will not be
> > awaken when events come on few tracers.
> >
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > ---
> > kernel/trace/trace.c | 2 ++
> > kernel/trace/trace_branch.c | 2 ++
> > kernel/trace/trace_hw_branches.c | 2 ++
> > 3 files changed, 6 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index e1f3b99..7f450b6 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -3055,6 +3055,8 @@ int trace_vprintk(unsigned long ip, int depth, const char *fmt, va_list args)
> > out:
> > preempt_enable_notrace();
> >
> > + trace_wake_up();
> > +
> > return len;
> > }
> > EXPORT_SYMBOL_GPL(trace_vprintk);
> > diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
> > index c2e68d4..8c8f8c0 100644
> > --- a/kernel/trace/trace_branch.c
> > +++ b/kernel/trace/trace_branch.c
> > @@ -78,6 +78,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
> > out:
> > atomic_dec(&tr->data[cpu]->disabled);
> > local_irq_restore(flags);
> > +
> > + trace_wake_up();
> > }
> >
> > static inline
> > diff --git a/kernel/trace/trace_hw_branches.c b/kernel/trace/trace_hw_branches.c
> > index 3561aac..ddd87fd 100644
> > --- a/kernel/trace/trace_hw_branches.c
> > +++ b/kernel/trace/trace_hw_branches.c
> > @@ -202,6 +202,8 @@ void trace_hw_branch(u64 from, u64 to)
> > out:
> > atomic_dec(&tr->data[cpu]->disabled);
> > local_irq_restore(irq1);
> > +
> > + trace_wake_up();
> > }
> >
> > static void trace_bts_at(const struct bts_trace *trace, void *at)
>
> Ah, we don't wake up purposely on these three places. ftrace_printk is
> meant to be called anywhere (including the scheduler). And the branch
> tracers are also allowed to be called anywhere (they usually are).
>
> Calling "wake_up" from any of these can easily cause a dead lock with the
> run queue lock, because all three can be called from with in the
> scheduler.
>
> Sorry, but I have to NACK this change.

Perhaps we could add these callsites back, but we would need to update
trace_wake_up.

Have trace_wake_up set a flag instead, and add a tracepoint around the
scheduler (outside the grabbing of runqueue locks), that will have a
callback to the tracing code. That call back can perform the wakeups.

How does that sound?

-- Steve