From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Thu, 8 Aug 2019 20:39:56 +0000 (-0400)
Subject: Fix: initialize kernel stream max subbuffer size on creation
X-Git-Tag: v2.12.0-rc1~512
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=d05185faf74eddb5d0425822efc877c6c0ce5f0a;p=lttng-tools.git

Fix: initialize kernel stream max subbuffer size on creation

A consumer stream's maximal subbuffer size is only initialized while
taking a snapshot. This unexpectedly leaves the max_sb_size at 0
causing the rotation target sequence number computation to crash with
a SIGFPE.

This fix initializes the value as soon as possible to provide a
behaviour in line with that of the ust-consumer.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/common/kernel-consumer/kernel-consumer.c b/src/common/kernel-consumer/kernel-consumer.c
index 29ccd0f09..9742ea084 100644
--- a/src/common/kernel-consumer/kernel-consumer.c
+++ b/src/common/kernel-consumer/kernel-consumer.c
@@ -231,15 +231,6 @@ static int lttng_kconsumer_snapshot_channel(
 			goto end_unlock;
 		}
 
-		if (stream->max_sb_size == 0) {
-			ret = kernctl_get_max_subbuf_size(stream->wait_fd,
-					&stream->max_sb_size);
-			if (ret < 0) {
-				ERR("Getting kernel max_sb_size");
-				goto end_unlock;
-			}
-		}
-
 		consumed_pos = consumer_get_consume_start_pos(consumed_pos,
 				produced_pos, nb_packets_per_stream,
 				stream->max_sb_size);
@@ -668,6 +659,14 @@ int lttng_kconsumer_recv_cmd(struct lttng_consumer_local_data *ctx,
 
 		new_stream->chan = channel;
 		new_stream->wait_fd = fd;
+		ret = kernctl_get_max_subbuf_size(new_stream->wait_fd,
+				&new_stream->max_sb_size);
+		if (ret < 0) {
+			pthread_mutex_unlock(&channel->lock);
+			ERR("Failed to get kernel maximal subbuffer size");
+			goto end_nosignal;
+		}
+
 		consumer_stream_update_channel_attributes(new_stream,
 				channel);
 		switch (channel->output) {