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    SubjectRe: [PATCH] tracing/ftrace: add missing wake-up on some callsites
    On Mon, Feb 23, 2009 at 10:42:04AM -0500, Steven Rostedt wrote:
    >
    > 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?


    That sounds good but only for these particular tracers I guess.


    > -- Steve
    >



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