relayd_live_stop performs, in this order:
CMM_STORE_SHARED(live_dispatch_thread_exit, 1); [A]
futex_nto1_wake(&viewer_conn_queue.futex); [B]
whereas thread_dispatcher does:
while (!CMM_LOAD_SHARED(live_dispatch_thread_exit)) { [1]
[...]
futex_nto1_prepare(&viewer_conn_queue.futex); [2]
[...]
futex_nto1_wait(&viewer_conn_queue.futex); [3]
Unfortunately, on the following sequence:
[1] [A] [B] [2] [3]
thread_dispatcher will end up hanging.
We need to move the live_dispatch_thread_exit load between "prepare" and
"wait" to fix this.
There are similar scenarios with relay_thread_dispatcher, and the
session daemon thread_dispatch_ust_registration, which are also fixed
here.
Signed-off-by: Mathieu Desnoyers <[email protected]>
---
src/bin/lttng-relayd/live.c | 6 +++++-
src/bin/lttng-relayd/main.c | 6 +++++-
src/bin/lttng-sessiond/main.c | 6 +++++-
3 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/src/bin/lttng-relayd/live.c b/src/bin/lttng-relayd/live.c
index 61acafe..f00270b 100644
--- a/src/bin/lttng-relayd/live.c
+++ b/src/bin/lttng-relayd/live.c
@@ -654,12 +654,16 @@ void *thread_dispatcher(void *data)
health_code_update();
- while (!CMM_LOAD_SHARED(live_dispatch_thread_exit)) {
+ for (;;) {
health_code_update();
/* Atomically prepare the queue futex */
futex_nto1_prepare(&viewer_conn_queue.futex);
+ if (CMM_LOAD_SHARED(live_dispatch_thread_exit)) {
+ break;
+ }
+
do {
health_code_update();
diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index 2fcc60a..0eb8e28 100644
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -977,12 +977,16 @@ static void *relay_thread_dispatcher(void *data)
health_code_update();
- while (!CMM_LOAD_SHARED(dispatch_thread_exit)) {
+ for (;;) {
health_code_update();
/* Atomically prepare the queue futex */
futex_nto1_prepare(&relay_conn_queue.futex);
+ if (CMM_LOAD_SHARED(dispatch_thread_exit)) {
+ break;
+ }
+
do {
health_code_update();
diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index 9b6f70c..e282a9c 100644
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -1934,12 +1934,16 @@ static void *thread_dispatch_ust_registration(void
*data)
DBG("[thread] Dispatch UST command started");
- while (!CMM_LOAD_SHARED(dispatch_thread_exit)) {
+ for (;;) {
health_code_update();
/* Atomically prepare the queue futex */
futex_nto1_prepare(&ust_cmd_queue.futex);
+ if (CMM_LOAD_SHARED(dispatch_thread_exit)) {
+ break;
+ }
+
do {
struct ust_app *app = NULL;
ust_cmd = NULL;
--
2.1.4
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