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SubjectRe: [PATCH] tracing: wake up tasks reading trace_pipe on write to trace_marker
FromSteven Rostedt <>
DateFri, 06 Aug 2010 16:38:56 -0400
On Wed, 2010-07-28 at 00:44 +0200, Marcin Slusarz wrote:
> Currently we rely on other code periodically waking up trace reader.
> If there aren't any other data than markers, reader will never be woken up.
> Fix it.
>
> Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> ---
> kernel/trace/trace.c | 1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 086d363..02e04c8 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1520,6 +1520,7 @@ int trace_array_vprintk(struct trace_array *tr,
> if (!filter_check_discard(call, entry, buffer, event)) {
> ring_buffer_unlock_commit(buffer, event);
> ftrace_trace_stack(buffer, irq_flags, 6, pc);
> + trace_wake_up();
> }
>

This can't work. trace_printk() and friends must be able to be used
anywhere. This can cause race conditions with the rq locks in the
scheduler.

But you do bring up a good idea. That is, perhaps we should have a way
to attach to known safe tracepoints that we can hook to to check if a
wake up should happen or not.

-- Steve




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