[PATCH 5.19 147/717] tracing: Wake up waiters when tracing is disabled

Greg Kroah-Hartman
2022-10-22T07:50:00Z

From: Steven Rostedt (Google) <rostedt@goodmis.org>

commit 2b0fd9a59b7990c161fa1cb7b79edb22847c87c2 upstream.

When tracing is disabled, there's no reason that waiters should stay
waiting, wake them up, otherwise tasks get stuck when they should be
flushing the buffers.

Cc: stable@vger.kernel.org
Fixes: e30f53aad2202 ("tracing: Do not busy wait in buffer splice")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/trace.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -8334,6 +8334,10 @@ tracing_buffers_splice_read(struct file
if (ret)
goto out;

+ /* No need to wait after waking up when tracing is off */
+ if (!tracer_tracing_is_on(iter->tr))
+ goto out;
+
/* Make sure we see the new wait_index */
smp_rmb();
if (wait_index != iter->wait_index)
@@ -9043,6 +9047,8 @@ rb_simple_write(struct file *filp, const
tracer_tracing_off(tr);
if (tr->current_trace->stop)
tr->current_trace->stop(tr);
+ /* Wake up any waiters */
+ ring_buffer_wake_waiters(buffer, RING_BUFFER_ALL_CPUS);
}
mutex_unlock(&trace_types_lock);
}