* [PATCH lttng-tools 1/2] Fix: filter attach vs event enable race
@ 2014-11-12 23:18 Mathieu Desnoyers
0 siblings, 0 replies; 2+ messages in thread
From: Mathieu Desnoyers @ 2014-11-12 23:18 UTC (permalink / raw)
To: jgalar; +Cc: lttng-dev
In order to correctly handle the use-case where events are enabled
_after_ trace is started, and _after_ applications are already being
traced, the event should be created in a "disabled" state, so that it
does not trace events until its filter is attached.
This fix needs to be done both in lttng-tools and lttng-ust. In order to
keep ABI compatibility between tools and ust within a stable release
cycle, we introduce a new "disabled" within struct lttng_ust_event
padding (previously zeroed). Newer LTTng-UST checks this flag, and
fallback on the old racy behavior (enabling the event on creation) if it
is unset.
Therefore, old session daemon works with newer lttng-ust of the same
stable release, and vice-versa. However, building lttng-tools requires
an upgraded lttng-ust, which contains the communication protocol with
the new "disabled" field.
This patch should be backported to stable-2.4, stable-2.5, stable-2.6
branches.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
src/bin/lttng-sessiond/trace-ust.c | 5 +++++
src/bin/lttng-sessiond/ust-app.c | 27 ++++++++++++++++++++++++++-
2 files changed, 31 insertions(+), 1 deletion(-)
diff --git a/src/bin/lttng-sessiond/trace-ust.c b/src/bin/lttng-sessiond/trace-ust.c
index 1f6fd52..ac980fd 100644
--- a/src/bin/lttng-sessiond/trace-ust.c
+++ b/src/bin/lttng-sessiond/trace-ust.c
@@ -419,6 +419,11 @@ struct ltt_ust_event *trace_ust_create_event(struct lttng_event *ev,
ERR("Unknown ust loglevel type (%d)", ev->loglevel_type);
goto error_free_event;
}
+ /*
+ * Fix for enabler race. Enable is now done explicitly by
+ * sessiond after setting filter.
+ */
+ lue->attr.disabled = 1;
/* Same layout. */
lue->filter_expression = filter_expression;
diff --git a/src/bin/lttng-sessiond/ust-app.c b/src/bin/lttng-sessiond/ust-app.c
index 5ebe991..7e4bf94 100644
--- a/src/bin/lttng-sessiond/ust-app.c
+++ b/src/bin/lttng-sessiond/ust-app.c
@@ -1446,7 +1446,32 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
}
/* If event not enabled, disable it on the tracer */
- if (ua_event->enabled == 0) {
+ if (ua_event->enabled) {
+ /*
+ * We now need to explicitly enable the event, since it
+ * is now disabled at creation.
+ */
+ ret = enable_ust_event(app, ua_sess, ua_event);
+ if (ret < 0) {
+ /*
+ * If we hit an EPERM, something is wrong with our enable call. If
+ * we get an EEXIST, there is a problem on the tracer side since we
+ * just created it.
+ */
+ switch (ret) {
+ case -LTTNG_UST_ERR_PERM:
+ /* Code flow problem */
+ assert(0);
+ case -LTTNG_UST_ERR_EXIST:
+ /* It's OK for our use case. */
+ ret = 0;
+ break;
+ default:
+ break;
+ }
+ goto error;
+ }
+ } else {
ret = disable_ust_event(app, ua_sess, ua_event);
if (ret < 0) {
/*
--
2.1.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH lttng-tools 1/2] Fix: filter attach vs event enable race
[not found] <1415834313-10400-1-git-send-email-mathieu.desnoyers@efficios.com>
@ 2014-11-17 17:05 ` Jérémie Galarneau
0 siblings, 0 replies; 2+ messages in thread
From: Jérémie Galarneau @ 2014-11-17 17:05 UTC (permalink / raw)
To: Mathieu Desnoyers; +Cc: lttng-dev, Jeremie Galarneau
Merged all the way back to 2.4, thanks!
Jérémie
On Wed, Nov 12, 2014 at 6:18 PM, Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
> In order to correctly handle the use-case where events are enabled
> _after_ trace is started, and _after_ applications are already being
> traced, the event should be created in a "disabled" state, so that it
> does not trace events until its filter is attached.
>
> This fix needs to be done both in lttng-tools and lttng-ust. In order to
> keep ABI compatibility between tools and ust within a stable release
> cycle, we introduce a new "disabled" within struct lttng_ust_event
> padding (previously zeroed). Newer LTTng-UST checks this flag, and
> fallback on the old racy behavior (enabling the event on creation) if it
> is unset.
>
> Therefore, old session daemon works with newer lttng-ust of the same
> stable release, and vice-versa. However, building lttng-tools requires
> an upgraded lttng-ust, which contains the communication protocol with
> the new "disabled" field.
>
> This patch should be backported to stable-2.4, stable-2.5, stable-2.6
> branches.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> ---
> src/bin/lttng-sessiond/trace-ust.c | 5 +++++
> src/bin/lttng-sessiond/ust-app.c | 27 ++++++++++++++++++++++++++-
> 2 files changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/src/bin/lttng-sessiond/trace-ust.c b/src/bin/lttng-sessiond/trace-ust.c
> index 1f6fd52..ac980fd 100644
> --- a/src/bin/lttng-sessiond/trace-ust.c
> +++ b/src/bin/lttng-sessiond/trace-ust.c
> @@ -419,6 +419,11 @@ struct ltt_ust_event *trace_ust_create_event(struct lttng_event *ev,
> ERR("Unknown ust loglevel type (%d)", ev->loglevel_type);
> goto error_free_event;
> }
> + /*
> + * Fix for enabler race. Enable is now done explicitly by
> + * sessiond after setting filter.
> + */
> + lue->attr.disabled = 1;
>
> /* Same layout. */
> lue->filter_expression = filter_expression;
> diff --git a/src/bin/lttng-sessiond/ust-app.c b/src/bin/lttng-sessiond/ust-app.c
> index 5ebe991..7e4bf94 100644
> --- a/src/bin/lttng-sessiond/ust-app.c
> +++ b/src/bin/lttng-sessiond/ust-app.c
> @@ -1446,7 +1446,32 @@ int create_ust_event(struct ust_app *app, struct ust_app_session *ua_sess,
> }
>
> /* If event not enabled, disable it on the tracer */
> - if (ua_event->enabled == 0) {
> + if (ua_event->enabled) {
> + /*
> + * We now need to explicitly enable the event, since it
> + * is now disabled at creation.
> + */
> + ret = enable_ust_event(app, ua_sess, ua_event);
> + if (ret < 0) {
> + /*
> + * If we hit an EPERM, something is wrong with our enable call. If
> + * we get an EEXIST, there is a problem on the tracer side since we
> + * just created it.
> + */
> + switch (ret) {
> + case -LTTNG_UST_ERR_PERM:
> + /* Code flow problem */
> + assert(0);
> + case -LTTNG_UST_ERR_EXIST:
> + /* It's OK for our use case. */
> + ret = 0;
> + break;
> + default:
> + break;
> + }
> + goto error;
> + }
> + } else {
> ret = disable_ust_event(app, ua_sess, ua_event);
> if (ret < 0) {
> /*
> --
> 2.1.1
>
--
Jérémie Galarneau
EfficiOS Inc.
http://www.efficios.com
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2014-11-12 23:18 [PATCH lttng-tools 1/2] Fix: filter attach vs event enable race Mathieu Desnoyers
[not found] <1415834313-10400-1-git-send-email-mathieu.desnoyers@efficios.com>
2014-11-17 17:05 ` Jérémie Galarneau
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