Fix: locking order between consumer and stream

Also, lock the stream BEFORE calling the read subbuffer so not to race
with the data pending command.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>

diff --git a/src/common/consumer.c b/src/common/consumer.c
index 260779ae6d1ace6d9a186c40c2202a654c85dbea..0e73bc9b8aeda6766953fbd381fcc05c370f795c 100644 (file)
--- a/src/common/consumer.c
+++ b/src/common/consumer.c
@@ -348,8 +348,8 @@ void consumer_del_stream(struct lttng_consumer_stream *stream,
                goto free_stream;
        }
 
-       pthread_mutex_lock(&stream->lock);
        pthread_mutex_lock(&consumer_data.lock);
+       pthread_mutex_lock(&stream->lock);
 
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
@@ -441,8 +441,8 @@ void consumer_del_stream(struct lttng_consumer_stream *stream,
 
 end:
        consumer_data.need_update = 1;
-       pthread_mutex_unlock(&consumer_data.lock);
        pthread_mutex_unlock(&stream->lock);
+       pthread_mutex_unlock(&consumer_data.lock);
 
        if (free_chan) {
                consumer_del_channel(free_chan);
@@ -1280,8 +1280,6 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
        /* RCU lock for the relayd pointer */
        rcu_read_lock();
 
-       pthread_mutex_lock(&stream->lock);
-
        /* Flag that the current stream if set for network streaming. */
        if (stream->net_seq_idx != -1) {
                relayd = consumer_find_relayd(stream->net_seq_idx);
@@ -1406,7 +1404,6 @@ end:
        if (relayd && stream->metadata_flag) {
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
        }
-       pthread_mutex_unlock(&stream->lock);
 
        rcu_read_unlock();
        return written;
@@ -1447,8 +1444,6 @@ ssize_t lttng_consumer_on_read_subbuffer_splice(
        /* RCU lock for the relayd pointer */
        rcu_read_lock();
 
-       pthread_mutex_lock(&stream->lock);
-
        /* Flag that the current stream if set for network streaming. */
        if (stream->net_seq_idx != -1) {
                relayd = consumer_find_relayd(stream->net_seq_idx);
@@ -1616,7 +1611,6 @@ end:
        if (relayd && stream->metadata_flag) {
                pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
        }
-       pthread_mutex_unlock(&stream->lock);
 
        rcu_read_unlock();
        return written;
@@ -1762,9 +1756,9 @@ void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
                goto free_stream;
        }
 
+       pthread_mutex_lock(&consumer_data.lock);
        pthread_mutex_lock(&stream->lock);
 
-       pthread_mutex_lock(&consumer_data.lock);
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
                if (stream->mmap_base != NULL) {
@@ -1854,8 +1848,8 @@ void consumer_del_metadata_stream(struct lttng_consumer_stream *stream,
        }
 
 end:
-       pthread_mutex_unlock(&consumer_data.lock);
        pthread_mutex_unlock(&stream->lock);
+       pthread_mutex_unlock(&consumer_data.lock);
 
        if (free_chan) {
                consumer_del_channel(free_chan);
@@ -2559,17 +2553,27 @@ end:
 ssize_t lttng_consumer_read_subbuffer(struct lttng_consumer_stream *stream,
                struct lttng_consumer_local_data *ctx)
 {
+       ssize_t ret;
+
+       pthread_mutex_lock(&stream->lock);
+
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
-               return lttng_kconsumer_read_subbuffer(stream, ctx);
+               ret = lttng_kconsumer_read_subbuffer(stream, ctx);
+               break;
        case LTTNG_CONSUMER32_UST:
        case LTTNG_CONSUMER64_UST:
-               return lttng_ustconsumer_read_subbuffer(stream, ctx);
+               ret = lttng_ustconsumer_read_subbuffer(stream, ctx);
+               break;
        default:
                ERR("Unknown consumer_data type");
                assert(0);
-               return -ENOSYS;
+               ret = -ENOSYS;
+               break;
        }
+
+       pthread_mutex_unlock(&stream->lock);
+       return ret;
 }
 
 int lttng_consumer_on_recv_stream(struct lttng_consumer_stream *stream)

diff --git a/src/common/consumer.h b/src/common/consumer.h
index 8411ff96463aab27773eb85123b8bac4e6369415..87ba490d7500af8ea078cec6ab652495ab5c91d5 100644 (file)
--- a/src/common/consumer.h
+++ b/src/common/consumer.h
@@ -132,10 +132,10 @@ struct lttng_consumer_stream {
        /* Next sequence number to use for trace packet */
        uint64_t next_net_seq_num;
        /*
-        * Lock to use the stream FDs since they are used between threads. Using
-        * this lock with network streaming, when using the control mutex of a
-        * consumer_relayd_sock_pair, make sure to acquire this lock BEFORE locking
-        * it and releasing it AFTER the control mutex unlock.
+        * Lock to use the stream FDs since they are used between threads.
+        *
+        * This is nested INSIDE the consumer_data lock.
+        * This is nested OUTSIDE consumer_relayd_sock_pair lock.
         */
        pthread_mutex_t lock;
        /* Tracing session id */
@@ -170,6 +170,9 @@ struct consumer_relayd_sock_pair {
         * between threads sending data to the relayd. Since metadata data is sent
         * over that socket, at least two sendmsg() are needed (header + data)
         * creating a race for packets to overlap between threads using it.
+        *
+        * This is nested INSIDE the consumer_data lock.
+        * This is nested INSIDE the stream lock.
         */
        pthread_mutex_t ctrl_sock_mutex;
 
@@ -257,8 +260,8 @@ struct lttng_consumer_global_data {
         * and number of element in the hash table. It's also a protection for
         * concurrent read/write between threads.
         *
-        * XXX: We need to see if this lock is still needed with the lockless RCU
-        * hash tables.
+        * This is nested OUTSIDE the stream lock.
+        * This is nested OUTSIDE the consumer_relayd_sock_pair lock.
         */
        pthread_mutex_t lock;