From: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Date: Thu, 7 Oct 2021 20:19:41 +0000 (-0400)
Subject: Fix: sessiond: previously created channel cannot be enabled
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=11ab4aee8e985a1b1fa05b8f788d4563d36f2ee2;p=lttng-tools.git

Fix: sessiond: previously created channel cannot be enabled

Observed issue
==============

A previously created channel cannot be enabled back once a session is
started.

Cause
=====

The check validating that the session was started is to early in the
`cmd_enable_channel` function.

Solution
========

Move the check at the creation code path when the channel is not found.

Known drawbacks
=========

None.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Change-Id: I8e7d62b7e97246e65f1cf9022270293a6dd34cc9
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
index 3b776c576..a7990ece4 100644
--- a/src/bin/lttng-sessiond/cmd.c
+++ b/src/bin/lttng-sessiond/cmd.c
@@ -1387,15 +1387,6 @@ int cmd_enable_channel(struct ltt_session *session,
 
 	rcu_read_lock();
 
-	/*
-	 * Don't try to enable a channel if the session has been started at
-	 * some point in time before. The tracer does not allow it.
-	 */
-	if (session->has_been_started) {
-		ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
-		goto error;
-	}
-
 	/*
 	 * If the session is a live session, remove the switch timer, the
 	 * live timer does the same thing but sends also synchronisation
@@ -1444,6 +1435,15 @@ int cmd_enable_channel(struct ltt_session *session,
 		kchan = trace_kernel_get_channel_by_name(attr.name,
 				session->kernel_session);
 		if (kchan == NULL) {
+			/*
+			 * Don't try to create a channel if the session has been started at
+			 * some point in time before. The tracer does not allow it.
+			 */
+			if (session->has_been_started) {
+				ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
+				goto error;
+			}
+
 			if (session->snapshot.nb_output > 0 ||
 					session->snapshot_mode) {
 				/* Enforce mmap output for snapshot sessions. */
@@ -1503,6 +1503,15 @@ int cmd_enable_channel(struct ltt_session *session,
 
 		uchan = trace_ust_find_channel_by_name(chan_ht, attr.name);
 		if (uchan == NULL) {
+			/*
+			 * Don't try to create a channel if the session has been started at
+			 * some point in time before. The tracer does not allow it.
+			 */
+			if (session->has_been_started) {
+				ret = LTTNG_ERR_TRACE_ALREADY_STARTED;
+				goto error;
+			}
+
 			ret = channel_ust_create(usess, &attr, domain->buf_type);
 			if (attr.name[0] != '\0') {
 				usess->has_non_default_channel = 1;