From 75df6e688ccd517e339a7c422ef7ad73045b18a2 Mon Sep 17 00:00:00 2001
From: Tahsin Erdogan <tahsin@google.com>
Date: Sun, 17 Sep 2017 03:23:48 -0700
Subject: [PATCH] tracing: Fix trace_pipe behavior for instance traces
Git-commit: 75df6e688ccd517e339a7c422ef7ad73045b18a2
Patch-mainline: v4.14-rc2
References: bsc#1120088

When reading data from trace_pipe, tracing_wait_pipe() performs a
check to see if tracing has been turned off after some data was read.
Currently, this check always looks at global trace state, but it
should be checking the trace instance where trace_pipe is located at.

Because of this bug, cat instances/i1/trace_pipe in the following
script will immediately exit instead of waiting for data:

cd /sys/kernel/debug/tracing
echo 0 > tracing_on
mkdir -p instances/i1
echo 1 > instances/i1/tracing_on
echo 1 > instances/i1/events/sched/sched_process_exec/enable
cat instances/i1/trace_pipe

Link: http://lkml.kernel.org/r/20170917102348.1615-1-tahsin@google.com

Cc: stable@vger.kernel.org
Fixes: 10246fa35d4f ("tracing: give easy way to clear trace buffer")
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Petr Mladek <pmladek@suse.com>

---
 kernel/trace/trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index d3ca35f38803..752e5daf0896 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5680,7 +5680,7 @@ static int tracing_wait_pipe(struct file *filp)
 		 *
 		 * iter->pos will be 0 if we haven't read anything.
 		 */
-		if (!tracing_is_on() && iter->pos)
+		if (!tracer_tracing_is_on(iter->tr) && iter->pos)
 			break;
 
 		mutex_unlock(&iter->mutex);
-- 
2.13.7