Fix: Lock metadata cache on session destroy

[lttng-modules.git] / lttng-events.c

diff --git a/lttng-events.c b/lttng-events.c
index d78e8efabe50fdf87f55dfbb6ede91176bbc4b9f..bb72156a8d4ce97c07290c70bf1e077fbcf7d907 100644 (file)
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -199,8 +199,10 @@ void lttng_session_destroy(struct lttng_session *session)
                BUG_ON(chan->channel_type == METADATA_CHANNEL);
                _lttng_channel_destroy(chan);
        }
+       mutex_lock(&session->metadata_cache->lock);
        list_for_each_entry(metadata_stream, &session->metadata_cache->metadata_stream, list)
                _lttng_metadata_channel_hangup(metadata_stream);
+       mutex_unlock(&session->metadata_cache->lock);
        if (session->pid_tracker)
                lttng_pid_tracker_destroy(session->pid_tracker);
        kref_put(&session->metadata_cache->refcount, metadata_cache_destroy);
@@ -1588,7 +1590,7 @@ void lttng_session_lazy_sync_enablers(struct lttng_session *session)
  * was written and a negative value on error.
  */
 int lttng_metadata_output_channel(struct lttng_metadata_stream *stream,
-               struct channel *chan)
+               struct channel *chan, bool *coherent)
 {
        struct lib_ring_buffer_ctx ctx;
        int ret = 0;
@@ -1627,6 +1629,7 @@ int lttng_metadata_output_channel(struct lttng_metadata_stream *stream,
        ret = stream->transport->ops.event_reserve(&ctx, 0);
        if (ret != 0) {
                printk(KERN_WARNING "LTTng: Metadata event reservation failed\n");
+               stream->coherent = false;
                goto end;
        }
        stream->transport->ops.event_write(&ctx,
@@ -1634,18 +1637,46 @@ int lttng_metadata_output_channel(struct lttng_metadata_stream *stream,
                        reserve_len);
        stream->transport->ops.event_commit(&ctx);
        stream->metadata_in += reserve_len;
+       if (reserve_len < len)
+               stream->coherent = false;
+       else
+               stream->coherent = true;
        ret = reserve_len;
 
 end:
+       if (coherent)
+               *coherent = stream->coherent;
        mutex_unlock(&stream->metadata_cache->lock);
        return ret;
 }
 
+static
+void lttng_metadata_begin(struct lttng_session *session)
+{
+       if (atomic_inc_return(&session->metadata_cache->producing) == 1)
+               mutex_lock(&session->metadata_cache->lock);
+}
+
+static
+void lttng_metadata_end(struct lttng_session *session)
+{
+       WARN_ON_ONCE(!atomic_read(&session->metadata_cache->producing));
+       if (atomic_dec_return(&session->metadata_cache->producing) == 0) {
+               struct lttng_metadata_stream *stream;
+
+               list_for_each_entry(stream, &session->metadata_cache->metadata_stream, list)
+                       wake_up_interruptible(&stream->read_wait);
+               mutex_unlock(&session->metadata_cache->lock);
+       }
+}
+
 /*
  * Write the metadata to the metadata cache.
  * Must be called with sessions_mutex held.
  * The metadata cache lock protects us from concurrent read access from
  * thread outputting metadata content to ring buffer.
+ * The content of the printf is printed as a single atomic metadata
+ * transaction.
  */
 int lttng_metadata_printf(struct lttng_session *session,
                          const char *fmt, ...)
@@ -1653,7 +1684,6 @@ int lttng_metadata_printf(struct lttng_session *session,
        char *str;
        size_t len;
        va_list ap;
-       struct lttng_metadata_stream *stream;
 
        WARN_ON_ONCE(!READ_ONCE(session->active));
 
@@ -1664,7 +1694,7 @@ int lttng_metadata_printf(struct lttng_session *session,
                return -ENOMEM;
 
        len = strlen(str);
-       mutex_lock(&session->metadata_cache->lock);
+       WARN_ON_ONCE(!atomic_read(&session->metadata_cache->producing));
        if (session->metadata_cache->metadata_written + len >
                        session->metadata_cache->cache_alloc) {
                char *tmp_cache_realloc;
@@ -1690,16 +1720,11 @@ int lttng_metadata_printf(struct lttng_session *session,
                        session->metadata_cache->metadata_written,
                        str, len);
        session->metadata_cache->metadata_written += len;
-       mutex_unlock(&session->metadata_cache->lock);
        kfree(str);
 
-       list_for_each_entry(stream, &session->metadata_cache->metadata_stream, list)
-               wake_up_interruptible(&stream->read_wait);
-
        return 0;
 
 err:
-       mutex_unlock(&session->metadata_cache->lock);
        kfree(str);
        return -ENOMEM;
 }
@@ -2236,6 +2261,8 @@ int _lttng_fields_metadata_statedump(struct lttng_session *session,
 
 /*
  * Must be called with sessions_mutex held.
+ * The entire event metadata is printed as a single atomic metadata
+ * transaction.
  */
 static
 int _lttng_event_metadata_statedump(struct lttng_session *session,
@@ -2249,6 +2276,8 @@ int _lttng_event_metadata_statedump(struct lttng_session *session,
        if (chan->channel_type == METADATA_CHANNEL)
                return 0;
 
+       lttng_metadata_begin(session);
+
        ret = lttng_metadata_printf(session,
                "event {\n"
                "       name = \"%s\";\n"
@@ -2298,12 +2327,15 @@ int _lttng_event_metadata_statedump(struct lttng_session *session,
 
        event->metadata_dumped = 1;
 end:
+       lttng_metadata_end(session);
        return ret;
 
 }
 
 /*
  * Must be called with sessions_mutex held.
+ * The entire channel metadata is printed as a single atomic metadata
+ * transaction.
  */
 static
 int _lttng_channel_metadata_statedump(struct lttng_session *session,
@@ -2317,6 +2349,8 @@ int _lttng_channel_metadata_statedump(struct lttng_session *session,
        if (chan->channel_type == METADATA_CHANNEL)
                return 0;
 
+       lttng_metadata_begin(session);
+
        WARN_ON_ONCE(!chan->header_type);
        ret = lttng_metadata_printf(session,
                "stream {\n"
@@ -2350,6 +2384,7 @@ int _lttng_channel_metadata_statedump(struct lttng_session *session,
 
        chan->metadata_dumped = 1;
 end:
+       lttng_metadata_end(session);
        return ret;
 }
 
@@ -2536,6 +2571,9 @@ int _lttng_session_metadata_statedump(struct lttng_session *session)
 
        if (!READ_ONCE(session->active))
                return 0;
+
+       lttng_metadata_begin(session);
+
        if (session->metadata_dumped)
                goto skip_session;
 
@@ -2697,6 +2735,7 @@ skip_session:
        }
        session->metadata_dumped = 1;
 end:
+       lttng_metadata_end(session);
        return ret;
 }