Fix: Missing rcu read side lock in consumer
[lttng-tools.git] / src / common / consumer.c
index deebd2e2b353cd1cc4365f5ede45e78203e9653e..a2980e77d29c33b57c4a12889cb82db019956fa0 100644 (file)
 #include <sys/socket.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <inttypes.h>
 
 #include <common/common.h>
+#include <common/utils.h>
+#include <common/compat/poll.h>
 #include <common/kernel-ctl/kernel-ctl.h>
 #include <common/sessiond-comm/relayd.h>
 #include <common/sessiond-comm/sessiond-comm.h>
@@ -172,7 +175,7 @@ static void consumer_rcu_free_relayd(struct rcu_head *head)
  *
  * This function MUST be called with the consumer_data lock acquired.
  */
-void consumer_destroy_relayd(struct consumer_relayd_sock_pair *relayd)
+static void destroy_relayd(struct consumer_relayd_sock_pair *relayd)
 {
        int ret;
        struct lttng_ht_iter iter;
@@ -200,6 +203,25 @@ void consumer_destroy_relayd(struct consumer_relayd_sock_pair *relayd)
        call_rcu(&relayd->node.head, consumer_rcu_free_relayd);
 }
 
+/*
+ * Flag a relayd socket pair for destruction. Destroy it if the refcount
+ * reaches zero.
+ *
+ * RCU read side lock MUST be aquired before calling this function.
+ */
+void consumer_flag_relayd_for_destroy(struct consumer_relayd_sock_pair *relayd)
+{
+       assert(relayd);
+
+       /* Set destroy flag for this object */
+       uatomic_set(&relayd->destroy_flag, 1);
+
+       /* Destroy the relayd if refcount is 0 */
+       if (uatomic_read(&relayd->refcount) == 0) {
+               destroy_relayd(relayd);
+       }
+}
+
 /*
  * Remove a stream from the global list protected by a mutex. This
  * function is also responsible for freeing its data structures.
@@ -274,9 +296,12 @@ void consumer_del_stream(struct lttng_consumer_stream *stream)
                uatomic_dec(&relayd->refcount);
                assert(uatomic_read(&relayd->refcount) >= 0);
 
+               /* Closing streams requires to lock the control socket. */
+               pthread_mutex_lock(&relayd->ctrl_sock_mutex);
                ret = relayd_send_close_stream(&relayd->control_sock,
                                stream->relayd_stream_id,
                                stream->next_net_seq_num - 1);
+               pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
                if (ret < 0) {
                        DBG("Unable to close stream on the relayd. Continuing");
                        /*
@@ -289,7 +314,7 @@ void consumer_del_stream(struct lttng_consumer_stream *stream)
                /* Both conditions are met, we destroy the relayd. */
                if (uatomic_read(&relayd->refcount) == 0 &&
                                uatomic_read(&relayd->destroy_flag)) {
-                       consumer_destroy_relayd(relayd);
+                       destroy_relayd(relayd);
                }
        }
        rcu_read_unlock();
@@ -417,20 +442,6 @@ int consumer_add_stream(struct lttng_consumer_stream *stream)
        consumer_data.stream_count++;
        consumer_data.need_update = 1;
 
-       switch (consumer_data.type) {
-       case LTTNG_CONSUMER_KERNEL:
-               break;
-       case LTTNG_CONSUMER32_UST:
-       case LTTNG_CONSUMER64_UST:
-               /* Streams are in CPU number order (we rely on this) */
-               stream->cpu = stream->chan->nr_streams++;
-               break;
-       default:
-               ERR("Unknown consumer_data type");
-               assert(0);
-               goto end;
-       }
-
 end:
        pthread_mutex_unlock(&consumer_data.lock);
 
@@ -438,9 +449,10 @@ end:
 }
 
 /*
- * Add relayd socket to global consumer data hashtable.
+ * Add relayd socket to global consumer data hashtable. RCU read side lock MUST
+ * be acquired before calling this.
  */
-int consumer_add_relayd(struct consumer_relayd_sock_pair *relayd)
+static int add_relayd(struct consumer_relayd_sock_pair *relayd)
 {
        int ret = 0;
        struct lttng_ht_node_ulong *node;
@@ -451,20 +463,15 @@ int consumer_add_relayd(struct consumer_relayd_sock_pair *relayd)
                goto end;
        }
 
-       rcu_read_lock();
-
        lttng_ht_lookup(consumer_data.relayd_ht,
                        (void *)((unsigned long) relayd->net_seq_idx), &iter);
        node = lttng_ht_iter_get_node_ulong(&iter);
        if (node != NULL) {
-               rcu_read_unlock();
                /* Relayd already exist. Ignore the insertion */
                goto end;
        }
        lttng_ht_add_unique_ulong(consumer_data.relayd_ht, &relayd->node);
 
-       rcu_read_unlock();
-
 end:
        return ret;
 }
@@ -534,7 +541,8 @@ error:
  * Return destination file descriptor or negative value on error.
  */
 static int write_relayd_stream_header(struct lttng_consumer_stream *stream,
-               size_t data_size, struct consumer_relayd_sock_pair *relayd)
+               size_t data_size, unsigned long padding,
+               struct consumer_relayd_sock_pair *relayd)
 {
        int outfd = -1, ret;
        struct lttcomm_relayd_data_hdr data_hdr;
@@ -559,6 +567,7 @@ static int write_relayd_stream_header(struct lttng_consumer_stream *stream,
                /* Set header with stream information */
                data_hdr.stream_id = htobe64(stream->relayd_stream_id);
                data_hdr.data_size = htobe32(data_size);
+               data_hdr.padding_size = htobe32(padding);
                data_hdr.net_seq_num = htobe64(stream->next_net_seq_num++);
                /* Other fields are zeroed previously */
 
@@ -678,7 +687,6 @@ struct lttng_consumer_channel *consumer_allocate_channel(
        channel->mmap_len = mmap_len;
        channel->max_sb_size = max_sb_size;
        channel->refcount = 0;
-       channel->nr_streams = 0;
        lttng_ht_node_init_ulong(&channel->node, channel->key);
 
        switch (consumer_data.type) {
@@ -746,8 +754,7 @@ end:
  */
 int consumer_update_poll_array(
                struct lttng_consumer_local_data *ctx, struct pollfd **pollfd,
-               struct lttng_consumer_stream **local_stream,
-               struct lttng_ht *metadata_ht)
+               struct lttng_consumer_stream **local_stream)
 {
        int i = 0;
        struct lttng_ht_iter iter;
@@ -763,10 +770,6 @@ int consumer_update_poll_array(
                DBG("Active FD %d", stream->wait_fd);
                (*pollfd)[i].fd = stream->wait_fd;
                (*pollfd)[i].events = POLLIN | POLLPRI;
-               if (stream->metadata_flag && metadata_ht) {
-                       lttng_ht_add_unique_ulong(metadata_ht, &stream->waitfd_node);
-                       DBG("Active FD added to metadata hash table");
-               }
                local_stream[i] = stream;
                i++;
        }
@@ -1005,9 +1008,22 @@ struct lttng_consumer_local_data *lttng_consumer_create(
                goto error_thread_pipe;
        }
 
-       return ctx;
+       ret = utils_create_pipe(ctx->consumer_metadata_pipe);
+       if (ret < 0) {
+               goto error_metadata_pipe;
+       }
+
+       ret = utils_create_pipe(ctx->consumer_splice_metadata_pipe);
+       if (ret < 0) {
+               goto error_splice_pipe;
+       }
 
+       return ctx;
 
+error_splice_pipe:
+       utils_close_pipe(ctx->consumer_metadata_pipe);
+error_metadata_pipe:
+       utils_close_pipe(ctx->consumer_thread_pipe);
 error_thread_pipe:
        for (i = 0; i < 2; i++) {
                int err;
@@ -1068,6 +1084,8 @@ void lttng_consumer_destroy(struct lttng_consumer_local_data *ctx)
        if (ret) {
                PERROR("close");
        }
+       utils_close_pipe(ctx->consumer_splice_metadata_pipe);
+
        unlink(ctx->consumer_command_sock_path);
        free(ctx);
 }
@@ -1077,22 +1095,23 @@ void lttng_consumer_destroy(struct lttng_consumer_local_data *ctx)
  */
 static int write_relayd_metadata_id(int fd,
                struct lttng_consumer_stream *stream,
-               struct consumer_relayd_sock_pair *relayd)
+               struct consumer_relayd_sock_pair *relayd,
+               unsigned long padding)
 {
        int ret;
-       uint64_t metadata_id;
+       struct lttcomm_relayd_metadata_payload hdr;
 
-       metadata_id = htobe64(stream->relayd_stream_id);
+       hdr.stream_id = htobe64(stream->relayd_stream_id);
+       hdr.padding_size = htobe32(padding);
        do {
-               ret = write(fd, (void *) &metadata_id,
-                               sizeof(stream->relayd_stream_id));
+               ret = write(fd, (void *) &hdr, sizeof(hdr));
        } while (ret < 0 && errno == EINTR);
        if (ret < 0) {
                PERROR("write metadata stream id");
                goto end;
        }
-       DBG("Metadata stream id %zu written before data",
-                       stream->relayd_stream_id);
+       DBG("Metadata stream id %" PRIu64 " with padding %lu written before data",
+                       stream->relayd_stream_id, padding);
 
 end:
        return ret;
@@ -1109,7 +1128,8 @@ end:
  */
 ssize_t lttng_consumer_on_read_subbuffer_mmap(
                struct lttng_consumer_local_data *ctx,
-               struct lttng_consumer_stream *stream, unsigned long len)
+               struct lttng_consumer_stream *stream, unsigned long len,
+               unsigned long padding)
 {
        unsigned long mmap_offset;
        ssize_t ret = 0, written = 0;
@@ -1161,17 +1181,17 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                if (stream->metadata_flag) {
                        /* Metadata requires the control socket. */
                        pthread_mutex_lock(&relayd->ctrl_sock_mutex);
-                       netlen += sizeof(stream->relayd_stream_id);
+                       netlen += sizeof(struct lttcomm_relayd_metadata_payload);
                }
 
-               ret = write_relayd_stream_header(stream, netlen, relayd);
+               ret = write_relayd_stream_header(stream, netlen, padding, relayd);
                if (ret >= 0) {
                        /* Use the returned socket. */
                        outfd = ret;
 
                        /* Write metadata stream id before payload */
                        if (stream->metadata_flag) {
-                               ret = write_relayd_metadata_id(outfd, stream, relayd);
+                               ret = write_relayd_metadata_id(outfd, stream, relayd, padding);
                                if (ret < 0) {
                                        written = ret;
                                        goto end;
@@ -1179,12 +1199,16 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                        }
                }
                /* Else, use the default set before which is the filesystem. */
+       } else {
+               /* No streaming, we have to set the len with the full padding */
+               len += padding;
        }
 
        while (len > 0) {
                do {
                        ret = write(outfd, stream->mmap_base + mmap_offset, len);
                } while (ret < 0 && errno == EINTR);
+               DBG("Consumer mmap write() ret %zd (len %lu)", ret, len);
                if (ret < 0) {
                        PERROR("Error in file write");
                        if (written == 0) {
@@ -1192,14 +1216,13 @@ ssize_t lttng_consumer_on_read_subbuffer_mmap(
                        }
                        goto end;
                } else if (ret > len) {
-                       PERROR("Error in file write (ret %ld > len %lu)", ret, len);
+                       PERROR("Error in file write (ret %zd > len %lu)", ret, len);
                        written += ret;
                        goto end;
                } else {
                        len -= ret;
                        mmap_offset += ret;
                }
-               DBG("Consumer mmap write() ret %ld (len %lu)", ret, len);
 
                /* This call is useless on a socket so better save a syscall. */
                if (!relayd) {
@@ -1229,7 +1252,8 @@ end:
  */
 ssize_t lttng_consumer_on_read_subbuffer_splice(
                struct lttng_consumer_local_data *ctx,
-               struct lttng_consumer_stream *stream, unsigned long len)
+               struct lttng_consumer_stream *stream, unsigned long len,
+               unsigned long padding)
 {
        ssize_t ret = 0, written = 0, ret_splice = 0;
        loff_t offset = 0;
@@ -1238,6 +1262,7 @@ ssize_t lttng_consumer_on_read_subbuffer_splice(
        /* Default is on the disk */
        int outfd = stream->out_fd;
        struct consumer_relayd_sock_pair *relayd = NULL;
+       int *splice_pipe;
 
        switch (consumer_data.type) {
        case LTTNG_CONSUMER_KERNEL:
@@ -1262,26 +1287,55 @@ ssize_t lttng_consumer_on_read_subbuffer_splice(
                }
        }
 
+       /*
+        * Choose right pipe for splice. Metadata and trace data are handled by
+        * different threads hence the use of two pipes in order not to race or
+        * corrupt the written data.
+        */
+       if (stream->metadata_flag) {
+               splice_pipe = ctx->consumer_splice_metadata_pipe;
+       } else {
+               splice_pipe = ctx->consumer_thread_pipe;
+       }
+
        /* Write metadata stream id before payload */
-       if (stream->metadata_flag && relayd) {
-               /*
-                * Lock the control socket for the complete duration of the function
-                * since from this point on we will use the socket.
-                */
-               pthread_mutex_lock(&relayd->ctrl_sock_mutex);
+       if (relayd) {
+               int total_len = len;
 
-               ret = write_relayd_metadata_id(ctx->consumer_thread_pipe[1],
-                               stream, relayd);
-               if (ret < 0) {
-                       written = ret;
+               if (stream->metadata_flag) {
+                       /*
+                        * Lock the control socket for the complete duration of the function
+                        * since from this point on we will use the socket.
+                        */
+                       pthread_mutex_lock(&relayd->ctrl_sock_mutex);
+
+                       ret = write_relayd_metadata_id(splice_pipe[1], stream, relayd,
+                                       padding);
+                       if (ret < 0) {
+                               written = ret;
+                               goto end;
+                       }
+
+                       total_len += sizeof(struct lttcomm_relayd_metadata_payload);
+               }
+
+               ret = write_relayd_stream_header(stream, total_len, padding, relayd);
+               if (ret >= 0) {
+                       /* Use the returned socket. */
+                       outfd = ret;
+               } else {
+                       ERR("Remote relayd disconnected. Stopping");
                        goto end;
                }
+       } else {
+               /* No streaming, we have to set the len with the full padding */
+               len += padding;
        }
 
        while (len > 0) {
-               DBG("splice chan to pipe offset %lu of len %lu (fd : %d)",
-                               (unsigned long)offset, len, fd);
-               ret_splice = splice(fd, &offset, ctx->consumer_thread_pipe[1], NULL, len,
+               DBG("splice chan to pipe offset %lu of len %lu (fd : %d, pipe: %d)",
+                               (unsigned long)offset, len, fd, splice_pipe[1]);
+               ret_splice = splice(fd, &offset, splice_pipe[1], NULL, len,
                                SPLICE_F_MOVE | SPLICE_F_MORE);
                DBG("splice chan to pipe, ret %zd", ret_splice);
                if (ret_splice < 0) {
@@ -1296,30 +1350,24 @@ ssize_t lttng_consumer_on_read_subbuffer_splice(
                /* Handle stream on the relayd if the output is on the network */
                if (relayd) {
                        if (stream->metadata_flag) {
+                               size_t metadata_payload_size =
+                                       sizeof(struct lttcomm_relayd_metadata_payload);
+
                                /* Update counter to fit the spliced data */
-                               ret_splice += sizeof(stream->relayd_stream_id);
-                               len += sizeof(stream->relayd_stream_id);
+                               ret_splice += metadata_payload_size;
+                               len += metadata_payload_size;
                                /*
                                 * We do this so the return value can match the len passed as
                                 * argument to this function.
                                 */
-                               written -= sizeof(stream->relayd_stream_id);
-                       }
-
-                       ret = write_relayd_stream_header(stream, ret_splice, relayd);
-                       if (ret >= 0) {
-                               /* Use the returned socket. */
-                               outfd = ret;
-                       } else {
-                               ERR("Remote relayd disconnected. Stopping");
-                               goto end;
+                               written -= metadata_payload_size;
                        }
                }
 
                /* Splice data out */
-               ret_splice = splice(ctx->consumer_thread_pipe[0], NULL, outfd, NULL,
+               ret_splice = splice(splice_pipe[0], NULL, outfd, NULL,
                                ret_splice, SPLICE_F_MOVE | SPLICE_F_MORE);
-               DBG("Kernel consumer splice pipe to file, ret %zd", ret_splice);
+               DBG("Consumer splice pipe to file, ret %zd", ret_splice);
                if (ret_splice < 0) {
                        PERROR("Error in file splice");
                        if (written == 0) {
@@ -1356,16 +1404,16 @@ splice_error:
        /* send the appropriate error description to sessiond */
        switch (ret) {
        case EBADF:
-               lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_EBADF);
+               lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_EBADF);
                break;
        case EINVAL:
-               lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_EINVAL);
+               lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_EINVAL);
                break;
        case ENOMEM:
-               lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_ENOMEM);
+               lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_ENOMEM);
                break;
        case ESPIPE:
-               lttng_consumer_send_error(ctx, CONSUMERD_SPLICE_ESPIPE);
+               lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_SPLICE_ESPIPE);
                break;
        }
 
@@ -1439,6 +1487,341 @@ int lttng_consumer_recv_cmd(struct lttng_consumer_local_data *ctx,
        }
 }
 
+/*
+ * Iterate over all stream element of the hashtable and free them. This is race
+ * free since the hashtable received MUST be in a race free synchronization
+ * state. It's the caller responsability to make sure of that.
+ */
+static void destroy_stream_ht(struct lttng_ht *ht)
+{
+       int ret;
+       struct lttng_ht_iter iter;
+       struct lttng_consumer_stream *stream;
+
+       if (ht == NULL) {
+               return;
+       }
+
+       rcu_read_lock();
+       cds_lfht_for_each_entry(ht->ht, &iter.iter, stream, node.node) {
+               ret = lttng_ht_del(ht, &iter);
+               assert(!ret);
+
+               free(stream);
+       }
+       rcu_read_unlock();
+
+       lttng_ht_destroy(ht);
+}
+
+/*
+ * Clean up a metadata stream and free its memory.
+ */
+static void consumer_del_metadata_stream(struct lttng_consumer_stream *stream)
+{
+       int ret;
+       struct lttng_consumer_channel *free_chan = NULL;
+       struct consumer_relayd_sock_pair *relayd;
+
+       assert(stream);
+       /*
+        * This call should NEVER receive regular stream. It must always be
+        * metadata stream and this is crucial for data structure synchronization.
+        */
+       assert(stream->metadata_flag);
+
+       pthread_mutex_lock(&consumer_data.lock);
+       switch (consumer_data.type) {
+       case LTTNG_CONSUMER_KERNEL:
+               if (stream->mmap_base != NULL) {
+                       ret = munmap(stream->mmap_base, stream->mmap_len);
+                       if (ret != 0) {
+                               PERROR("munmap metadata stream");
+                       }
+               }
+               break;
+       case LTTNG_CONSUMER32_UST:
+       case LTTNG_CONSUMER64_UST:
+               lttng_ustconsumer_del_stream(stream);
+               break;
+       default:
+               ERR("Unknown consumer_data type");
+               assert(0);
+       }
+       pthread_mutex_unlock(&consumer_data.lock);
+
+       if (stream->out_fd >= 0) {
+               ret = close(stream->out_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+       }
+
+       if (stream->wait_fd >= 0 && !stream->wait_fd_is_copy) {
+               ret = close(stream->wait_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+       }
+
+       if (stream->shm_fd >= 0 && stream->wait_fd != stream->shm_fd) {
+               ret = close(stream->shm_fd);
+               if (ret) {
+                       PERROR("close");
+               }
+       }
+
+       /* Check and cleanup relayd */
+       rcu_read_lock();
+       relayd = consumer_find_relayd(stream->net_seq_idx);
+       if (relayd != NULL) {
+               uatomic_dec(&relayd->refcount);
+               assert(uatomic_read(&relayd->refcount) >= 0);
+
+               /* Closing streams requires to lock the control socket. */
+               pthread_mutex_lock(&relayd->ctrl_sock_mutex);
+               ret = relayd_send_close_stream(&relayd->control_sock,
+                               stream->relayd_stream_id, stream->next_net_seq_num - 1);
+               pthread_mutex_unlock(&relayd->ctrl_sock_mutex);
+               if (ret < 0) {
+                       DBG("Unable to close stream on the relayd. Continuing");
+                       /*
+                        * Continue here. There is nothing we can do for the relayd.
+                        * Chances are that the relayd has closed the socket so we just
+                        * continue cleaning up.
+                        */
+               }
+
+               /* Both conditions are met, we destroy the relayd. */
+               if (uatomic_read(&relayd->refcount) == 0 &&
+                               uatomic_read(&relayd->destroy_flag)) {
+                       destroy_relayd(relayd);
+               }
+       }
+       rcu_read_unlock();
+
+       /* Atomically decrement channel refcount since other threads can use it. */
+       uatomic_dec(&stream->chan->refcount);
+       if (!uatomic_read(&stream->chan->refcount)) {
+               free_chan = stream->chan;
+       }
+
+       if (free_chan) {
+               consumer_del_channel(free_chan);
+       }
+
+       free(stream);
+}
+
+/*
+ * Action done with the metadata stream when adding it to the consumer internal
+ * data structures to handle it.
+ */
+static void consumer_add_metadata_stream(struct lttng_consumer_stream *stream)
+{
+       struct consumer_relayd_sock_pair *relayd;
+
+       /* Find relayd and, if one is found, increment refcount. */
+       rcu_read_lock();
+       relayd = consumer_find_relayd(stream->net_seq_idx);
+       if (relayd != NULL) {
+               uatomic_inc(&relayd->refcount);
+       }
+       rcu_read_unlock();
+}
+
+/*
+ * Thread polls on metadata file descriptor and write them on disk or on the
+ * network.
+ */
+void *lttng_consumer_thread_poll_metadata(void *data)
+{
+       int ret, i, pollfd;
+       uint32_t revents, nb_fd;
+       struct lttng_consumer_stream *stream;
+       struct lttng_ht_iter iter;
+       struct lttng_ht_node_ulong *node;
+       struct lttng_ht *metadata_ht = NULL;
+       struct lttng_poll_event events;
+       struct lttng_consumer_local_data *ctx = data;
+       ssize_t len;
+
+       rcu_register_thread();
+
+       DBG("Thread metadata poll started");
+
+       metadata_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       if (metadata_ht == NULL) {
+               goto end;
+       }
+
+       /* Size is set to 1 for the consumer_metadata pipe */
+       ret = lttng_poll_create(&events, 2, LTTNG_CLOEXEC);
+       if (ret < 0) {
+               ERR("Poll set creation failed");
+               goto end;
+       }
+
+       ret = lttng_poll_add(&events, ctx->consumer_metadata_pipe[0], LPOLLIN);
+       if (ret < 0) {
+               goto end;
+       }
+
+       /* Main loop */
+       DBG("Metadata main loop started");
+
+       while (1) {
+               lttng_poll_reset(&events);
+
+               nb_fd = LTTNG_POLL_GETNB(&events);
+
+               /* Only the metadata pipe is set */
+               if (nb_fd == 0 && consumer_quit == 1) {
+                       goto end;
+               }
+
+restart:
+               DBG("Metadata poll wait with %d fd(s)", nb_fd);
+               ret = lttng_poll_wait(&events, -1);
+               DBG("Metadata event catched in thread");
+               if (ret < 0) {
+                       if (errno == EINTR) {
+                               goto restart;
+                       }
+                       goto error;
+               }
+
+               for (i = 0; i < nb_fd; i++) {
+                       revents = LTTNG_POLL_GETEV(&events, i);
+                       pollfd = LTTNG_POLL_GETFD(&events, i);
+
+                       /* Check the metadata pipe for incoming metadata. */
+                       if (pollfd == ctx->consumer_metadata_pipe[0]) {
+                               if (revents & (LPOLLERR | LPOLLHUP )) {
+                                       DBG("Metadata thread pipe hung up");
+                                       /*
+                                        * Remove the pipe from the poll set and continue the loop
+                                        * since their might be data to consume.
+                                        */
+                                       lttng_poll_del(&events, ctx->consumer_metadata_pipe[0]);
+                                       close(ctx->consumer_metadata_pipe[0]);
+                                       continue;
+                               } else if (revents & LPOLLIN) {
+                                       stream = zmalloc(sizeof(struct lttng_consumer_stream));
+                                       if (stream == NULL) {
+                                               PERROR("zmalloc metadata consumer stream");
+                                               goto error;
+                                       }
+
+                                       do {
+                                               /* Get the stream and add it to the local hash table */
+                                               ret = read(pollfd, stream,
+                                                               sizeof(struct lttng_consumer_stream));
+                                       } while (ret < 0 && errno == EINTR);
+                                       if (ret < 0 || ret < sizeof(struct lttng_consumer_stream)) {
+                                               PERROR("read metadata stream");
+                                               free(stream);
+                                               /*
+                                                * Let's continue here and hope we can still work
+                                                * without stopping the consumer. XXX: Should we?
+                                                */
+                                               continue;
+                                       }
+
+                                       DBG("Adding metadata stream %d to poll set",
+                                                       stream->wait_fd);
+
+                                       rcu_read_lock();
+                                       /* The node should be init at this point */
+                                       lttng_ht_add_unique_ulong(metadata_ht,
+                                                       &stream->waitfd_node);
+                                       rcu_read_unlock();
+
+                                       /* Add metadata stream to the global poll events list */
+                                       lttng_poll_add(&events, stream->wait_fd,
+                                                       LPOLLIN | LPOLLPRI);
+
+                                       consumer_add_metadata_stream(stream);
+                               }
+
+                               /* Metadata pipe handled. Continue handling the others */
+                               continue;
+                       }
+
+                       /* From here, the event is a metadata wait fd */
+
+                       rcu_read_lock();
+                       lttng_ht_lookup(metadata_ht, (void *)((unsigned long) pollfd),
+                                       &iter);
+                       node = lttng_ht_iter_get_node_ulong(&iter);
+                       if (node == NULL) {
+                               /* FD not found, continue loop */
+                               rcu_read_unlock();
+                               continue;
+                       }
+
+                       stream = caa_container_of(node, struct lttng_consumer_stream,
+                                       waitfd_node);
+
+                       /* Get the data out of the metadata file descriptor */
+                       if (revents & (LPOLLIN | LPOLLPRI)) {
+                               DBG("Metadata available on fd %d", pollfd);
+                               assert(stream->wait_fd == pollfd);
+
+                               len = ctx->on_buffer_ready(stream, ctx);
+                               /* It's ok to have an unavailable sub-buffer */
+                               if (len < 0 && len != -EAGAIN) {
+                                       rcu_read_unlock();
+                                       goto end;
+                               } else if (len > 0) {
+                                       stream->data_read = 1;
+                               }
+                       }
+
+                       /*
+                        * Remove the stream from the hash table since there is no data
+                        * left on the fd because we previously did a read on the buffer.
+                        */
+                       if (revents & (LPOLLERR | LPOLLHUP)) {
+                               DBG("Metadata fd %d is hup|err|nval.", pollfd);
+                               if (!stream->hangup_flush_done
+                                               && (consumer_data.type == LTTNG_CONSUMER32_UST
+                                                       || consumer_data.type == LTTNG_CONSUMER64_UST)) {
+                                       DBG("Attempting to flush and consume the UST buffers");
+                                       lttng_ustconsumer_on_stream_hangup(stream);
+
+                                       /* We just flushed the stream now read it. */
+                                       len = ctx->on_buffer_ready(stream, ctx);
+                                       /* It's ok to have an unavailable sub-buffer */
+                                       if (len < 0 && len != -EAGAIN) {
+                                               rcu_read_unlock();
+                                               goto end;
+                                       }
+                               }
+
+                               /* Removing it from hash table, poll set and free memory */
+                               lttng_ht_del(metadata_ht, &iter);
+
+                               lttng_poll_del(&events, stream->wait_fd);
+                               consumer_del_metadata_stream(stream);
+                       }
+                       rcu_read_unlock();
+               }
+       }
+
+error:
+end:
+       DBG("Metadata poll thread exiting");
+       lttng_poll_clean(&events);
+
+       if (metadata_ht) {
+               destroy_stream_ht(metadata_ht);
+       }
+
+       rcu_unregister_thread();
+       return NULL;
+}
+
 /*
  * This thread polls the fds in the set to consume the data and write
  * it to tracefile if necessary.
@@ -1452,16 +1835,20 @@ void *lttng_consumer_thread_poll_fds(void *data)
        /* local view of consumer_data.fds_count */
        int nb_fd = 0;
        struct lttng_consumer_local_data *ctx = data;
-       struct lttng_ht *metadata_ht;
-       struct lttng_ht_iter iter;
-       struct lttng_ht_node_ulong *node;
-       struct lttng_consumer_stream *metadata_stream;
        ssize_t len;
-
-       metadata_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
+       pthread_t metadata_thread;
+       void *status;
 
        rcu_register_thread();
 
+       /* Start metadata polling thread */
+       ret = pthread_create(&metadata_thread, NULL,
+                       lttng_consumer_thread_poll_metadata, (void *) ctx);
+       if (ret < 0) {
+               PERROR("pthread_create metadata thread");
+               goto end;
+       }
+
        local_stream = zmalloc(sizeof(struct lttng_consumer_stream));
 
        while (1) {
@@ -1499,11 +1886,10 @@ void *lttng_consumer_thread_poll_fds(void *data)
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }
-                       ret = consumer_update_poll_array(ctx, &pollfd, local_stream,
-                                       metadata_ht);
+                       ret = consumer_update_poll_array(ctx, &pollfd, local_stream);
                        if (ret < 0) {
                                ERR("Error in allocating pollfd or local_outfds");
-                               lttng_consumer_send_error(ctx, CONSUMERD_POLL_ERROR);
+                               lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_POLL_ERROR);
                                pthread_mutex_unlock(&consumer_data.lock);
                                goto end;
                        }
@@ -1529,7 +1915,7 @@ void *lttng_consumer_thread_poll_fds(void *data)
                                goto restart;
                        }
                        perror("Poll error");
-                       lttng_consumer_send_error(ctx, CONSUMERD_POLL_ERROR);
+                       lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_POLL_ERROR);
                        goto end;
                } else if (num_rdy == 0) {
                        DBG("Polling thread timed out");
@@ -1555,24 +1941,7 @@ void *lttng_consumer_thread_poll_fds(void *data)
 
                /* Take care of high priority channels first. */
                for (i = 0; i < nb_fd; i++) {
-                       /* Lookup for metadata which is the highest priority */
-                       lttng_ht_lookup(metadata_ht,
-                                       (void *)((unsigned long) pollfd[i].fd), &iter);
-                       node = lttng_ht_iter_get_node_ulong(&iter);
-                       if (node != NULL &&
-                                       (pollfd[i].revents & (POLLIN | POLLPRI))) {
-                               DBG("Urgent metadata read on fd %d", pollfd[i].fd);
-                               metadata_stream = caa_container_of(node,
-                                               struct lttng_consumer_stream, waitfd_node);
-                               high_prio = 1;
-                               len = ctx->on_buffer_ready(metadata_stream, ctx);
-                               /* it's ok to have an unavailable sub-buffer */
-                               if (len < 0 && len != -EAGAIN) {
-                                       goto end;
-                               } else if (len > 0) {
-                                       metadata_stream->data_read = 1;
-                               }
-                       } else if (pollfd[i].revents & POLLPRI) {
+                       if (pollfd[i].revents & POLLPRI) {
                                DBG("Urgent read on fd %d", pollfd[i].fd);
                                high_prio = 1;
                                len = ctx->on_buffer_ready(local_stream[i], ctx);
@@ -1628,33 +1997,18 @@ void *lttng_consumer_thread_poll_fds(void *data)
                        if ((pollfd[i].revents & POLLHUP)) {
                                DBG("Polling fd %d tells it has hung up.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
-                                       if (local_stream[i]->metadata_flag) {
-                                               iter.iter.node = &local_stream[i]->waitfd_node.node;
-                                               ret = lttng_ht_del(metadata_ht, &iter);
-                                               assert(!ret);
-                                       }
                                        consumer_del_stream(local_stream[i]);
                                        num_hup++;
                                }
                        } else if (pollfd[i].revents & POLLERR) {
                                ERR("Error returned in polling fd %d.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
-                                       if (local_stream[i]->metadata_flag) {
-                                               iter.iter.node = &local_stream[i]->waitfd_node.node;
-                                               ret = lttng_ht_del(metadata_ht, &iter);
-                                               assert(!ret);
-                                       }
                                        consumer_del_stream(local_stream[i]);
                                        num_hup++;
                                }
                        } else if (pollfd[i].revents & POLLNVAL) {
                                ERR("Polling fd %d tells fd is not open.", pollfd[i].fd);
                                if (!local_stream[i]->data_read) {
-                                       if (local_stream[i]->metadata_flag) {
-                                               iter.iter.node = &local_stream[i]->waitfd_node.node;
-                                               ret = lttng_ht_del(metadata_ht, &iter);
-                                               assert(!ret);
-                                       }
                                        consumer_del_stream(local_stream[i]);
                                        num_hup++;
                                }
@@ -1672,6 +2026,23 @@ end:
                free(local_stream);
                local_stream = NULL;
        }
+
+       /*
+        * Close the write side of the pipe so epoll_wait() in
+        * lttng_consumer_thread_poll_metadata can catch it. The thread is
+        * monitoring the read side of the pipe. If we close them both, epoll_wait
+        * strangely does not return and could create a endless wait period if the
+        * pipe is the only tracked fd in the poll set. The thread will take care
+        * of closing the read side.
+        */
+       close(ctx->consumer_metadata_pipe[1]);
+       if (ret) {
+               ret = pthread_join(metadata_thread, &status);
+               if (ret < 0) {
+                       PERROR("pthread_join metadata thread");
+               }
+       }
+
        rcu_unregister_thread();
        return NULL;
 }
@@ -1706,7 +2077,7 @@ void *lttng_consumer_thread_receive_fds(void *data)
        }
 
        DBG("Sending ready command to lttng-sessiond");
-       ret = lttng_consumer_send_error(ctx, CONSUMERD_COMMAND_SOCK_READY);
+       ret = lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_COMMAND_SOCK_READY);
        /* return < 0 on error, but == 0 is not fatal */
        if (ret < 0) {
                ERR("Error sending ready command to lttng-sessiond");
@@ -1756,8 +2127,12 @@ void *lttng_consumer_thread_receive_fds(void *data)
                        DBG("Received STOP command");
                        goto end;
                }
-               if (ret < 0) {
-                       ERR("Communication interrupted on command socket");
+               if (ret <= 0) {
+                       /*
+                        * This could simply be a session daemon quitting. Don't output
+                        * ERR() here.
+                        */
+                       DBG("Communication interrupted on command socket");
                        goto end;
                }
                if (consumer_quit) {
@@ -1840,3 +2215,95 @@ void lttng_consumer_init(void)
        consumer_data.channel_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
        consumer_data.relayd_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
 }
+
+/*
+ * Process the ADD_RELAYD command receive by a consumer.
+ *
+ * This will create a relayd socket pair and add it to the relayd hash table.
+ * The caller MUST acquire a RCU read side lock before calling it.
+ */
+int consumer_add_relayd_socket(int net_seq_idx, int sock_type,
+               struct lttng_consumer_local_data *ctx, int sock,
+               struct pollfd *consumer_sockpoll, struct lttcomm_sock *relayd_sock)
+{
+       int fd, ret = -1;
+       struct consumer_relayd_sock_pair *relayd;
+
+       DBG("Consumer adding relayd socket (idx: %d)", net_seq_idx);
+
+       /* Get relayd reference if exists. */
+       relayd = consumer_find_relayd(net_seq_idx);
+       if (relayd == NULL) {
+               /* Not found. Allocate one. */
+               relayd = consumer_allocate_relayd_sock_pair(net_seq_idx);
+               if (relayd == NULL) {
+                       lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_OUTFD_ERROR);
+                       goto error;
+               }
+       }
+
+       /* Poll on consumer socket. */
+       if (lttng_consumer_poll_socket(consumer_sockpoll) < 0) {
+               ret = -EINTR;
+               goto error;
+       }
+
+       /* Get relayd socket from session daemon */
+       ret = lttcomm_recv_fds_unix_sock(sock, &fd, 1);
+       if (ret != sizeof(fd)) {
+               lttng_consumer_send_error(ctx, LTTCOMM_CONSUMERD_ERROR_RECV_FD);
+               ret = -1;
+               goto error;
+       }
+
+       /* Copy socket information and received FD */
+       switch (sock_type) {
+       case LTTNG_STREAM_CONTROL:
+               /* Copy received lttcomm socket */
+               lttcomm_copy_sock(&relayd->control_sock, relayd_sock);
+               ret = lttcomm_create_sock(&relayd->control_sock);
+               if (ret < 0) {
+                       goto error;
+               }
+
+               /* Close the created socket fd which is useless */
+               close(relayd->control_sock.fd);
+
+               /* Assign new file descriptor */
+               relayd->control_sock.fd = fd;
+               break;
+       case LTTNG_STREAM_DATA:
+               /* Copy received lttcomm socket */
+               lttcomm_copy_sock(&relayd->data_sock, relayd_sock);
+               ret = lttcomm_create_sock(&relayd->data_sock);
+               if (ret < 0) {
+                       goto error;
+               }
+
+               /* Close the created socket fd which is useless */
+               close(relayd->data_sock.fd);
+
+               /* Assign new file descriptor */
+               relayd->data_sock.fd = fd;
+               break;
+       default:
+               ERR("Unknown relayd socket type (%d)", sock_type);
+               goto error;
+       }
+
+       DBG("Consumer %s socket created successfully with net idx %d (fd: %d)",
+                       sock_type == LTTNG_STREAM_CONTROL ? "control" : "data",
+                       relayd->net_seq_idx, fd);
+
+       /*
+        * Add relayd socket pair to consumer data hashtable. If object already
+        * exists or on error, the function gracefully returns.
+        */
+       add_relayd(relayd);
+
+       /* All good! */
+       ret = 0;
+
+error:
+       return ret;
+}
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