tracing/ring-buffer: Have polling block on watermark

Currently the way polling works on the ring buffer is broken. It will
return immediately if there's any data in the ring buffer whereas a read
will block until the watermark (defined by the tracefs buffer_percent file)
is hit.

That is, a select() or poll() will return as if there's data available,
but then the following read will block. This is broken for the way
select()s and poll()s are supposed to work.

Have the polling on the ring buffer also block the same way reads and
splice does on the ring buffer.

Link: https://lkml.kernel.org/r/20221020231427.41be3f26@gandalf.local.home

Cc: Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Primiano Tucci <primiano@google.com>
Cc: stable@vger.kernel.org
Fixes: 1e0d6714aceb7 ("ring-buffer: Do not wake up a splice waiter when page is not full")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 47a44b055a1d..c6c7a0af3ed2 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6681,7 +6681,7 @@ trace_poll(struct trace_iterator *iter, struct file *filp, poll_table *poll_tabl
 		return EPOLLIN | EPOLLRDNORM;
 	else
 		return ring_buffer_poll_wait(iter->array_buffer->buffer, iter->cpu_file,
-					     filp, poll_table);
+					     filp, poll_table, iter->tr->buffer_percent);
 }
 
 static __poll_t