From: Michael Jeanson <mjeanson@efficios.com>
Date: Mon, 28 Oct 2024 20:02:59 +0000 (-0400)
Subject: Fix: silence 'non-consumed' message for non-started sessions
X-Git-Tag: v2.13.16~3
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=56f320664342ebf7b00376a2b813189484e22d6d;p=lttng-modules.git

Fix: silence 'non-consumed' message for non-started sessions

Destroying a session with at least one enabled event and which has never
been started will currently result in an error message in the kernel log
about 'non-consumed data' for each of the per-cpu buffer. This happens
because a packet header is created in the buffer but never consumed if
the session is not started.

Add a check in the buffer cleanup code to avoid printing 'non-consumed
data' errors for buffers associated with a session taht was never
started.

Change-Id: I1358e1ae49d03544a961515b97b115a488434e27
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/include/ringbuffer/frontend_types.h b/include/ringbuffer/frontend_types.h
index 07d23be2..4158033d 100644
--- a/include/ringbuffer/frontend_types.h
+++ b/include/ringbuffer/frontend_types.h
@@ -71,6 +71,7 @@ struct lttng_kernel_ring_buffer_channel {
 	int finalized;				/* Has channel been finalized */
 	struct channel_iter iter;		/* Channel read-side iterator */
 	struct kref ref;			/* Reference count */
+	int been_active;			/* Tracing was started at least once */
 };
 
 /* Per-subbuffer commit counters used on the hot path */
diff --git a/src/lib/ringbuffer/ring_buffer_frontend.c b/src/lib/ringbuffer/ring_buffer_frontend.c
index 468d3bbc..e5984e67 100644
--- a/src/lib/ringbuffer/ring_buffer_frontend.c
+++ b/src/lib/ringbuffer/ring_buffer_frontend.c
@@ -1502,7 +1502,13 @@ void lib_ring_buffer_print_buffer_errors(struct lttng_kernel_ring_buffer *buf,
 	 */
 	write_offset = v_read(config, &buf->offset);
 	cons_offset = atomic_long_read(&buf->consumed);
-	if (write_offset != cons_offset)
+
+	/*
+	 * Only print errors if the session associated with the buffer has been
+	 * active, otherwise destroying an un-started session results in errors
+	 * because of the un-consumed packet header present in the buffer.
+	 */
+	if (chan->been_active && write_offset != cons_offset)
 		printk(KERN_DEBUG
 		       "LTTng: ring buffer %s, cpu %d: "
 		       "non-consumed data\n"
diff --git a/src/lttng-events.c b/src/lttng-events.c
index 314fb3ec..e3ce3e74 100644
--- a/src/lttng-events.c
+++ b/src/lttng-events.c
@@ -499,6 +499,8 @@ int lttng_session_enable(struct lttng_kernel_session *session)
 	list_for_each_entry(chan_priv, &session->priv->chan, node) {
 		if (chan_priv->channel_type != METADATA_CHANNEL)
 			lib_ring_buffer_clear_quiescent_channel(chan_priv->rb_chan);
+
+		WRITE_ONCE(chan_priv->rb_chan->been_active, 1);
 	}
 
 	WRITE_ONCE(session->active, 1);