Patch "tracing: Fix trace_pipe behavior for instance traces" has been added to the 3.18-stable tree

Patch "tracing: Fix trace_pipe behavior for instance traces" has been added to the 3.18-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    tracing: Fix trace_pipe behavior for instance traces

to the 3.18-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     tracing-fix-trace_pipe-behavior-for-instance-traces.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>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: tracing: Fix trace_pipe behavior for instance traces

From: Tahsin Erdogan <tahsin@google.com>

commit 75df6e688ccd517e339a7c422ef7ad73045b18a2 upstream.

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

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4430,7 +4430,7 @@ static int tracing_wait_pipe(struct file
 		 *
 		 * 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);


Patches currently in stable-queue which might be from tahsin@google.com are

queue-3.18/tracing-fix-trace_pipe-behavior-for-instance-traces.patch