* David Goulet ([email protected]) wrote:
> Introduce a second hash table indexed by application socket which have
> the exact same content as the hash table indexed by PID.
> 
> On unregister, we now use a direct lookup per socket instead of using
> the key map between sock and PID. This prevent the PID-sock lookup race

prevent -> prevents

> when the unregister happens just after the replace and before the
> close(fd).
> 
> We also use an add_replace call on application registration.
> 
> (closes #7)
> 
> Signed-off-by: David Goulet <[email protected]>
> ---
>  src/bin/lttng-sessiond/ust-app.c |  246 
> ++++++++++++++++++--------------------
>  src/bin/lttng-sessiond/ust-app.h |   21 ++--
>  src/common/hashtable/hashtable.h |    4 +-
>  3 files changed, 131 insertions(+), 140 deletions(-)
> 
> diff --git a/src/bin/lttng-sessiond/ust-app.c 
> b/src/bin/lttng-sessiond/ust-app.c
> index 8e6d20e..645691d 100644
> --- a/src/bin/lttng-sessiond/ust-app.c
> +++ b/src/bin/lttng-sessiond/ust-app.c
> @@ -180,29 +180,28 @@ void delete_ust_app(struct ust_app *app)
>       rcu_read_lock();
>  
>       /* Delete ust app sessions info */
> -     sock = app->key.sock;
> -     app->key.sock = -1;
> +     sock = app->sock;
> +     app->sock = -1;
>  
>       /* Wipe sessions */
>       cds_lfht_for_each_entry(app->sessions->ht, &iter.iter, ua_sess,
>                       node.node) {
>               ret = lttng_ht_del(app->sessions, &iter);
>               assert(!ret);
> -             delete_ust_app_session(app->key.sock, ua_sess);
> +             delete_ust_app_session(app->sock, ua_sess);
>       }
>       lttng_ht_destroy(app->sessions);
>  
>       /*
> -      * Wait until we have removed the key from the sock hash table before
> -      * closing this socket, otherwise an application could re-use the 
> socket ID
> -      * and race with the teardown, using the same hash table entry.

Please keep the explanation above too, which explains the lifetime of
the socket ID uniqueness.

> +      * Closing socket free the value for another application to be added 
> with
> +      * the same socket value.
>        */
>       ret = close(sock);

Yep, it's OK to leave the close in call_rcu. We want it to stay unique
for all RCU readers that could run concurrently with unregister app,
therefore we _need_ to only close that socket after a grace period. So
it should stay in this RCU callback.

>       if (ret) {
>               PERROR("close");
>       }
>  
> -     DBG2("UST app pid %d deleted", app->key.pid);
> +     DBG2("UST app pid %d deleted", app->pid);
>       free(app);
>  
>       rcu_read_unlock();
> @@ -217,9 +216,9 @@ void delete_ust_app_rcu(struct rcu_head *head)
>       struct lttng_ht_node_ulong *node =
>               caa_container_of(head, struct lttng_ht_node_ulong, head);
>       struct ust_app *app =
> -             caa_container_of(node, struct ust_app, node);
> +             caa_container_of(node, struct ust_app, pid_n);
>  
> -     DBG3("Call RCU deleting app PID %d", app->key.pid);
> +     DBG3("Call RCU deleting app PID %d", app->pid);
>       delete_ust_app(app);
>  }
>  
> @@ -354,25 +353,16 @@ static
>  struct ust_app *find_app_by_sock(int sock)
>  {
>       struct lttng_ht_node_ulong *node;
> -     struct ust_app_key *key;
>       struct lttng_ht_iter iter;
>  
> -     lttng_ht_lookup(ust_app_sock_key_map, (void *)((unsigned long) sock),
> -                     &iter);
> -     node = lttng_ht_iter_get_node_ulong(&iter);
> -     if (node == NULL) {
> -             DBG2("UST app find by sock %d key not found", sock);
> -             goto error;
> -     }
> -     key = caa_container_of(node, struct ust_app_key, node);
> -
> -     lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) key->pid), &iter);
> +     lttng_ht_lookup(ust_app_ht_by_sock, (void *)((unsigned long) sock), 
> &iter);
>       node = lttng_ht_iter_get_node_ulong(&iter);
>       if (node == NULL) {
>               DBG2("UST app find by sock %d not found", sock);
>               goto error;
>       }
> -     return caa_container_of(node, struct ust_app, node);
> +
> +     return caa_container_of(node, struct ust_app, sock_n);
>  
>  error:
>       return NULL;
> @@ -387,7 +377,7 @@ int create_ust_channel_context(struct ust_app_channel 
> *ua_chan,
>  {
>       int ret;
>  
> -     ret = ustctl_add_context(app->key.sock, &ua_ctx->ctx,
> +     ret = ustctl_add_context(app->sock, &ua_ctx->ctx,
>                       ua_chan->obj, &ua_ctx->obj);
>       if (ret < 0) {
>               goto error;
> @@ -410,7 +400,7 @@ int create_ust_event_context(struct ust_app_event 
> *ua_event,
>  {
>       int ret;
>  
> -     ret = ustctl_add_context(app->key.sock, &ua_ctx->ctx,
> +     ret = ustctl_add_context(app->sock, &ua_ctx->ctx,
>                       ua_event->obj, &ua_ctx->obj);
>       if (ret < 0) {
>               goto error;
> @@ -432,16 +422,16 @@ static int disable_ust_event(struct ust_app *app,
>  {
>       int ret;
>  
> -     ret = ustctl_disable(app->key.sock, ua_event->obj);
> +     ret = ustctl_disable(app->sock, ua_event->obj);
>       if (ret < 0) {
>               ERR("UST app event %s disable failed for app (pid: %d) "
>                               "and session handle %d with ret %d",
> -                             ua_event->attr.name, app->key.pid, 
> ua_sess->handle, ret);
> +                             ua_event->attr.name, app->pid, ua_sess->handle, 
> ret);
>               goto error;
>       }
>  
>       DBG2("UST app event %s disabled successfully for app (pid: %d)",
> -                     ua_event->attr.name, app->key.pid);
> +                     ua_event->attr.name, app->pid);
>  
>  error:
>       return ret;
> @@ -455,16 +445,16 @@ static int disable_ust_channel(struct ust_app *app,
>  {
>       int ret;
>  
> -     ret = ustctl_disable(app->key.sock, ua_chan->obj);
> +     ret = ustctl_disable(app->sock, ua_chan->obj);
>       if (ret < 0) {
>               ERR("UST app channel %s disable failed for app (pid: %d) "
>                               "and session handle %d with ret %d",
> -                             ua_chan->name, app->key.pid, ua_sess->handle, 
> ret);
> +                             ua_chan->name, app->pid, ua_sess->handle, ret);
>               goto error;
>       }
>  
>       DBG2("UST app channel %s disabled successfully for app (pid: %d)",
> -                     ua_chan->name, app->key.pid);
> +                     ua_chan->name, app->pid);
>  
>  error:
>       return ret;
> @@ -478,18 +468,18 @@ static int enable_ust_channel(struct ust_app *app,
>  {
>       int ret;
>  
> -     ret = ustctl_enable(app->key.sock, ua_chan->obj);
> +     ret = ustctl_enable(app->sock, ua_chan->obj);
>       if (ret < 0) {
>               ERR("UST app channel %s enable failed for app (pid: %d) "
>                               "and session handle %d with ret %d",
> -                             ua_chan->name, app->key.pid, ua_sess->handle, 
> ret);
> +                             ua_chan->name, app->pid, ua_sess->handle, ret);
>               goto error;
>       }
>  
>       ua_chan->enabled = 1;
>  
>       DBG2("UST app channel %s enabled successfully for app (pid: %d)",
> -                     ua_chan->name, app->key.pid);
> +                     ua_chan->name, app->pid);
>  
>  error:
>       return ret;
> @@ -503,16 +493,16 @@ static int enable_ust_event(struct ust_app *app,
>  {
>       int ret;
>  
> -     ret = ustctl_enable(app->key.sock, ua_event->obj);
> +     ret = ustctl_enable(app->sock, ua_event->obj);
>       if (ret < 0) {
>               ERR("UST app event %s enable failed for app (pid: %d) "
>                               "and session handle %d with ret %d",
> -                             ua_event->attr.name, app->key.pid, 
> ua_sess->handle, ret);
> +                             ua_event->attr.name, app->pid, ua_sess->handle, 
> ret);
>               goto error;
>       }
>  
>       DBG2("UST app event %s enabled successfully for app (pid: %d)",
> -                     ua_event->attr.name, app->key.pid);
> +                     ua_event->attr.name, app->pid);
>  
>  error:
>       return ret;
> @@ -537,11 +527,11 @@ static int open_ust_metadata(struct ust_app *app,
>       uattr.output = ua_sess->metadata->attr.output;
>  
>       /* UST tracer metadata creation */
> -     ret = ustctl_open_metadata(app->key.sock, ua_sess->handle, &uattr,
> +     ret = ustctl_open_metadata(app->sock, ua_sess->handle, &uattr,
>                       &ua_sess->metadata->obj);
>       if (ret < 0) {
>               ERR("UST app open metadata failed for app pid:%d with ret %d",
> -                             app->key.pid, ret);
> +                             app->pid, ret);
>               goto error;
>       }
>  
> @@ -559,7 +549,7 @@ static int create_ust_stream(struct ust_app *app,
>  {
>       int ret;
>  
> -     ret = ustctl_create_stream(app->key.sock, ua_sess->metadata->obj,
> +     ret = ustctl_create_stream(app->sock, ua_sess->metadata->obj,
>                       &ua_sess->metadata->stream_obj);
>       if (ret < 0) {
>               ERR("UST create metadata stream failed");
> @@ -579,12 +569,12 @@ static int create_ust_channel(struct ust_app *app,
>       int ret;
>  
>       /* TODO: remove cast and use lttng-ust-abi.h */
> -     ret = ustctl_create_channel(app->key.sock, ua_sess->handle,
> +     ret = ustctl_create_channel(app->sock, ua_sess->handle,
>                       (struct lttng_ust_channel_attr *)&ua_chan->attr, 
> &ua_chan->obj);
>       if (ret < 0) {
>               ERR("Creating channel %s for app (pid: %d, sock: %d) "
>                               "and session handle %d with ret %d",
> -                             ua_chan->name, app->key.pid, app->key.sock,
> +                             ua_chan->name, app->pid, app->sock,
>                               ua_sess->handle, ret);
>               goto error;
>       }
> @@ -592,7 +582,7 @@ static int create_ust_channel(struct ust_app *app,
>       ua_chan->handle = ua_chan->obj->handle;
>  
>       DBG2("UST app channel %s created successfully for pid:%d and sock:%d",
> -                     ua_chan->name, app->key.pid, app->key.sock);
> +                     ua_chan->name, app->pid, app->sock);
>  
>       /* If channel is not enabled, disable it on the tracer */
>       if (!ua_chan->enabled) {
> @@ -616,7 +606,7 @@ int create_ust_event(struct ust_app *app, struct 
> ust_app_session *ua_sess,
>       int ret = 0;
>  
>       /* Create UST event on tracer */
> -     ret = ustctl_create_event(app->key.sock, &ua_event->attr, ua_chan->obj,
> +     ret = ustctl_create_event(app->sock, &ua_event->attr, ua_chan->obj,
>                       &ua_event->obj);
>       if (ret < 0) {
>               if (ret == -EEXIST) {
> @@ -624,14 +614,14 @@ int create_ust_event(struct ust_app *app, struct 
> ust_app_session *ua_sess,
>                       goto error;
>               }
>               ERR("Error ustctl create event %s for app pid: %d with ret %d",
> -                             ua_event->attr.name, app->key.pid, ret);
> +                             ua_event->attr.name, app->pid, ret);
>               goto error;
>       }
>  
>       ua_event->handle = ua_event->obj->handle;
>  
>       DBG2("UST app event %s created successfully for pid:%d",
> -                     ua_event->attr.name, app->key.pid);
> +                     ua_event->attr.name, app->pid);
>  
>       /* If event not enabled, disable it on the tracer */
>       if (ua_event->enabled == 0) {
> @@ -772,7 +762,7 @@ static void shadow_copy_session(struct ust_app_session 
> *ua_sess,
>       ua_sess->gid = usess->gid;
>  
>       ret = snprintf(ua_sess->path, PATH_MAX, "%s/%s-%d-%s", usess->pathname,
> -                     app->name, app->key.pid, datetime);
> +                     app->name, app->pid, datetime);
>       if (ret < 0) {
>               PERROR("asprintf UST shadow copy session");
>               /* TODO: We cannot return an error from here.. */
> @@ -854,7 +844,7 @@ static struct ust_app_session *create_ust_app_session(
>       ua_sess = lookup_session_by_app(usess, app);
>       if (ua_sess == NULL) {
>               DBG2("UST app pid: %d session id %d not found, creating it",
> -                             app->key.pid, usess->id);
> +                             app->pid, usess->id);
>               ua_sess = alloc_ust_app_session();
>               if (ua_sess == NULL) {
>                       /* Only malloc can failed so something is really wrong 
> */
> @@ -864,9 +854,9 @@ static struct ust_app_session *create_ust_app_session(
>       }
>  
>       if (ua_sess->handle == -1) {
> -             ret = ustctl_create_session(app->key.sock);
> +             ret = ustctl_create_session(app->sock);
>               if (ret < 0) {
> -                     ERR("Creating session for app pid %d", app->key.pid);
> +                     ERR("Creating session for app pid %d", app->pid);
>                       /* This means that the tracer is gone... */
>                       ua_sess = (void*) -1UL;
>                       goto error;
> @@ -1097,7 +1087,7 @@ static struct ust_app_channel *create_ust_app_channel(
>       lttng_ht_add_unique_str(ua_sess->channels, &ua_chan->node);
>  
>       DBG2("UST app create channel %s for PID %d completed", ua_chan->name,
> -                     app->key.pid);
> +                     app->pid);
>  
>  end:
>       return ua_chan;
> @@ -1148,7 +1138,7 @@ int create_ust_app_event(struct ust_app_session 
> *ua_sess,
>       lttng_ht_add_unique_str(ua_chan->events, &ua_event->node);
>  
>       DBG2("UST app create event %s for PID %d completed", ua_event->name,
> -                     app->key.pid);
> +                     app->pid);
>  
>  end:
>       return ret;
> @@ -1189,7 +1179,7 @@ static int create_ust_app_metadata(struct 
> ust_app_session *ua_sess,
>                       goto error;
>               }
>  
> -             DBG2("UST metadata opened for app pid %d", app->key.pid);
> +             DBG2("UST metadata opened for app pid %d", app->pid);
>       }
>  
>       /* Open UST metadata stream */
> @@ -1214,7 +1204,7 @@ static int create_ust_app_metadata(struct 
> ust_app_session *ua_sess,
>               }
>  
>               DBG2("UST metadata stream object created for app pid %d",
> -                             app->key.pid);
> +                             app->pid);
>       } else {
>               ERR("Attempting to create stream without metadata opened");
>               goto error;
> @@ -1253,7 +1243,7 @@ struct ust_app *ust_app_find_by_pid(pid_t pid)
>  
>       DBG2("Found UST app by pid %d", pid);
>  
> -     return caa_container_of(node, struct ust_app, node);
> +     return caa_container_of(node, struct ust_app, pid_n);
>  
>  error:
>       rcu_read_unlock();
> @@ -1310,20 +1300,19 @@ int ust_app_register(struct ust_register_msg *msg, 
> int sock)
>       lta->name[16] = '\0';
>       lta->sessions = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
>  
> -     /* Set key map */
> -     lta->key.pid = msg->pid;
> -     lttng_ht_node_init_ulong(&lta->node, (unsigned long)lta->key.pid);
> -     lta->key.sock = sock;
> -     lttng_ht_node_init_ulong(&lta->key.node, (unsigned long)lta->key.sock);
> +     lta->pid = msg->pid;
> +     lttng_ht_node_init_ulong(&lta->pid_n, (unsigned long)lta->pid);
> +     lta->sock = sock;
> +     lttng_ht_node_init_ulong(&lta->sock_n, (unsigned long)lta->sock);
>  
>       rcu_read_lock();
> -     lttng_ht_add_unique_ulong(ust_app_sock_key_map, &lta->key.node);
> -     lttng_ht_add_unique_ulong(ust_app_ht, &lta->node);
> +     lttng_ht_add_replace_ulong(ust_app_ht, &lta->pid_n);
> +     lttng_ht_add_replace_ulong(ust_app_ht_by_sock, &lta->sock_n);

add_replace is needed for the pid table, I agree with that
(re-registration, we want to kick out the previous registration of that
pid). However, for the socket hash table, the socket FD _should_ be
unique until _we_ call close. So we should keep a add_unique for the
ust_app_ht_by_sock, which asserts fail if the entry was already in the
table.

>       rcu_read_unlock();
>  
>       DBG("App registered with pid:%d ppid:%d uid:%d gid:%d sock:%d name:%s"
> -                     " (version %d.%d)", lta->key.pid, lta->ppid, lta->uid, 
> lta->gid,
> -                     lta->key.sock, lta->name, lta->v_major, lta->v_minor);
> +                     " (version %d.%d)", lta->pid, lta->ppid, lta->uid, 
> lta->gid,
> +                     lta->sock, lta->name, lta->v_major, lta->v_minor);
>  
>       return 0;
>  }
> @@ -1342,31 +1331,32 @@ void ust_app_unregister(int sock)
>       int ret;
>  
>       rcu_read_lock();
> -     lta = find_app_by_sock(sock);
> -     if (lta == NULL) {
> -             ERR("Unregister app sock %d not found!", sock);
> -             goto error;
> -     }
> -
> -     DBG("PID %d unregistering with sock %d", lta->key.pid, sock);
> -
> -     /* Remove application from socket hash table */
> -     lttng_ht_lookup(ust_app_sock_key_map, (void *)((unsigned long) sock), 
> &iter);
> -     ret = lttng_ht_del(ust_app_sock_key_map, &iter);
> -     assert(!ret);
>  
>       /* Get the node reference for a call_rcu */
> -     lttng_ht_lookup(ust_app_ht, (void *)((unsigned long) lta->key.pid), 
> &iter);
> +     lttng_ht_lookup(ust_app_ht_by_sock, (void *)((unsigned long) sock), 
> &iter);
>       node = lttng_ht_iter_get_node_ulong(&iter);
>       if (node == NULL) {
> -             ERR("Unable to find app sock %d by pid %d", sock, lta->key.pid);
> +             ERR("Unable to find app by sock %d", sock);
>               goto error;
>       }
>  
> +     lta = caa_container_of(node, struct ust_app, sock_n);
> +
> +     DBG("PID %d unregistering with sock %d", lta->pid, sock);
> +
>       /* Remove application from PID hash table */
> +     ret = lttng_ht_del(ust_app_ht_by_sock, &iter);
> +     assert(!ret);
> +
> +     /* Assign second node for deletion */
> +     iter.iter.node = &lta->pid_n.node;
> +
>       ret = lttng_ht_del(ust_app_ht, &iter);
>       assert(!ret);
> -     call_rcu(&node->head, delete_ust_app_rcu);
> +
> +     /* Free memory */
> +     call_rcu(&lta->pid_n.head, delete_ust_app_rcu);
> +
>  error:
>       rcu_read_unlock();
>       return;
> @@ -1407,7 +1397,7 @@ int ust_app_list_events(struct lttng_event **events)
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               struct lttng_ust_tracepoint_iter uiter;
>  
>               if (!app->compatible) {
> @@ -1417,14 +1407,14 @@ int ust_app_list_events(struct lttng_event **events)
>                        */
>                       continue;
>               }
> -             handle = ustctl_tracepoint_list(app->key.sock);
> +             handle = ustctl_tracepoint_list(app->sock);
>               if (handle < 0) {
>                       ERR("UST app list events getting handle failed for app 
> pid %d",
> -                                     app->key.pid);
> +                                     app->pid);
>                       continue;
>               }
>  
> -             while ((ret = ustctl_tracepoint_list_get(app->key.sock, handle,
> +             while ((ret = ustctl_tracepoint_list_get(app->sock, handle,
>                                               &uiter)) != -ENOENT) {
>                       if (count >= nbmem) {
>                               DBG2("Reallocating event list from %zu to %zu 
> entries", nbmem,
> @@ -1440,7 +1430,7 @@ int ust_app_list_events(struct lttng_event **events)
>                       memcpy(tmp[count].name, uiter.name, 
> LTTNG_UST_SYM_NAME_LEN);
>                       tmp[count].loglevel = uiter.loglevel;
>                       tmp[count].type = LTTNG_UST_TRACEPOINT;
> -                     tmp[count].pid = app->key.pid;
> +                     tmp[count].pid = app->pid;
>                       tmp[count].enabled = -1;
>                       count++;
>               }
> @@ -1475,15 +1465,15 @@ void ust_app_clean_list(void)
>               assert(!ret);
>               call_rcu(&node->head, delete_ust_app_rcu);
>       }
> +
>       /* Destroy is done only when the ht is empty */
>       lttng_ht_destroy(ust_app_ht);
>  
> -     cds_lfht_for_each_entry(ust_app_sock_key_map->ht, &iter.iter, node, 
> node) {
> -             ret = lttng_ht_del(ust_app_sock_key_map, &iter);
> -             assert(!ret);
> -     }
> -     /* Destroy is done only when the ht is empty */
> -     lttng_ht_destroy(ust_app_sock_key_map);
> +     /*
> +      * Emptying the previous hash table makes sure this table is also ready 
> for
> +      * destruction.
> +      */

I think you forgot to iterate on ust_app_ht_by_sock to invoke
lttng_ht_del of each node, before the destroy of the whole hash table.

Thanks,

Mathieu

> +     lttng_ht_destroy(ust_app_ht_by_sock);
>  
>       rcu_read_unlock();
>  }
> @@ -1494,7 +1484,7 @@ void ust_app_clean_list(void)
>  void ust_app_ht_alloc(void)
>  {
>       ust_app_ht = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
> -     ust_app_sock_key_map = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
> +     ust_app_ht_by_sock = lttng_ht_new(0, LTTNG_HT_TYPE_ULONG);
>  }
>  
>  /*
> @@ -1522,7 +1512,7 @@ int ust_app_disable_channel_glb(struct ltt_ust_session 
> *usess,
>       rcu_read_lock();
>  
>       /* For every registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               struct lttng_ht_iter uiter;
>               if (!app->compatible) {
>                       /*
> @@ -1583,7 +1573,7 @@ int ust_app_enable_channel_glb(struct ltt_ust_session 
> *usess,
>       rcu_read_lock();
>  
>       /* For every registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -1630,7 +1620,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session 
> *usess,
>       rcu_read_lock();
>  
>       /* For all registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -1649,7 +1639,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session 
> *usess,
>               ua_chan_node = lttng_ht_iter_get_node_str(&uiter);
>               if (ua_chan_node == NULL) {
>                       DBG2("Channel %s not found in session id %d for app pid 
> %d."
> -                                     "Skipping", uchan->name, usess->id, 
> app->key.pid);
> +                                     "Skipping", uchan->name, usess->id, 
> app->pid);
>                       continue;
>               }
>               ua_chan = caa_container_of(ua_chan_node, struct 
> ust_app_channel, node);
> @@ -1658,7 +1648,7 @@ int ust_app_disable_event_glb(struct ltt_ust_session 
> *usess,
>               ua_event_node = lttng_ht_iter_get_node_str(&uiter);
>               if (ua_event_node == NULL) {
>                       DBG2("Event %s not found in channel %s for app pid %d."
> -                                     "Skipping", uevent->attr.name, 
> uchan->name, app->key.pid);
> +                                     "Skipping", uevent->attr.name, 
> uchan->name, app->pid);
>                       continue;
>               }
>               ua_event = caa_container_of(ua_event_node, struct 
> ust_app_event, node);
> @@ -1696,7 +1686,7 @@ int ust_app_disable_all_event_glb(struct 
> ltt_ust_session *usess,
>       rcu_read_lock();
>  
>       /* For all registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -1753,7 +1743,7 @@ int ust_app_create_channel_glb(struct ltt_ust_session 
> *usess,
>       rcu_read_lock();
>  
>       /* For every registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -1817,7 +1807,7 @@ int ust_app_enable_event_glb(struct ltt_ust_session 
> *usess,
>       rcu_read_lock();
>  
>       /* For all registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -1841,7 +1831,7 @@ int ust_app_enable_event_glb(struct ltt_ust_session 
> *usess,
>               ua_event_node = lttng_ht_iter_get_node_str(&uiter);
>               if (ua_event_node == NULL) {
>                       DBG3("UST app enable event %s not found for app PID %d."
> -                                     "Skipping app", uevent->attr.name, 
> app->key.pid);
> +                                     "Skipping app", uevent->attr.name, 
> app->pid);
>                       continue;
>               }
>               ua_event = caa_container_of(ua_event_node, struct 
> ust_app_event, node);
> @@ -1877,7 +1867,7 @@ int ust_app_create_event_glb(struct ltt_ust_session 
> *usess,
>       rcu_read_lock();
>  
>       /* For all registered applications */
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -1904,7 +1894,7 @@ int ust_app_create_event_glb(struct ltt_ust_session 
> *usess,
>                               break;
>                       }
>                       DBG2("UST app event %s already exist on app PID %d",
> -                                     uevent->attr.name, app->key.pid);
> +                                     uevent->attr.name, app->pid);
>                       continue;
>               }
>       }
> @@ -1926,7 +1916,7 @@ int ust_app_start_trace(struct ltt_ust_session *usess, 
> struct ust_app *app)
>       struct ltt_ust_stream *ustream;
>       int consumerd_fd;
>  
> -     DBG("Starting tracing for ust app pid %d", app->key.pid);
> +     DBG("Starting tracing for ust app pid %d", app->pid);
>  
>       rcu_read_lock();
>  
> @@ -1964,7 +1954,7 @@ int ust_app_start_trace(struct ltt_ust_session *usess, 
> struct ust_app *app)
>                               goto error_rcu_unlock;
>                       }
>  
> -                     ret = ustctl_create_stream(app->key.sock, ua_chan->obj,
> +                     ret = ustctl_create_stream(app->sock, ua_chan->obj,
>                                       &ustream->obj);
>                       if (ret < 0) {
>                               /* Got all streams */
> @@ -2006,14 +1996,14 @@ int ust_app_start_trace(struct ltt_ust_session 
> *usess, struct ust_app *app)
>  
>  skip_setup:
>       /* This start the UST tracing */
> -     ret = ustctl_start_session(app->key.sock, ua_sess->handle);
> +     ret = ustctl_start_session(app->sock, ua_sess->handle);
>       if (ret < 0) {
> -             ERR("Error starting tracing for app pid: %d", app->key.pid);
> +             ERR("Error starting tracing for app pid: %d", app->pid);
>               goto error_rcu_unlock;
>       }
>  
>       /* Quiescent wait after starting trace */
> -     ustctl_wait_quiescent(app->key.sock);
> +     ustctl_wait_quiescent(app->sock);
>  
>  end:
>       rcu_read_unlock();
> @@ -2034,7 +2024,7 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, 
> struct ust_app *app)
>       struct ust_app_session *ua_sess;
>       struct ust_app_channel *ua_chan;
>  
> -     DBG("Stopping tracing for ust app pid %d", app->key.pid);
> +     DBG("Stopping tracing for ust app pid %d", app->pid);
>  
>       rcu_read_lock();
>  
> @@ -2056,31 +2046,31 @@ int ust_app_stop_trace(struct ltt_ust_session *usess, 
> struct ust_app *app)
>       assert(ua_sess->started == 1);
>  
>       /* This inhibits UST tracing */
> -     ret = ustctl_stop_session(app->key.sock, ua_sess->handle);
> +     ret = ustctl_stop_session(app->sock, ua_sess->handle);
>       if (ret < 0) {
> -             ERR("Error stopping tracing for app pid: %d", app->key.pid);
> +             ERR("Error stopping tracing for app pid: %d", app->pid);
>               goto error_rcu_unlock;
>       }
>  
>       /* Quiescent wait after stopping trace */
> -     ustctl_wait_quiescent(app->key.sock);
> +     ustctl_wait_quiescent(app->sock);
>  
>       /* Flushing buffers */
>       cds_lfht_for_each_entry(ua_sess->channels->ht, &iter.iter, ua_chan,
>                       node.node) {
> -             ret = ustctl_sock_flush_buffer(app->key.sock, ua_chan->obj);
> +             ret = ustctl_sock_flush_buffer(app->sock, ua_chan->obj);
>               if (ret < 0) {
>                       ERR("UST app PID %d channel %s flush failed with ret 
> %d",
> -                                     app->key.pid, ua_chan->name, ret);
> +                                     app->pid, ua_chan->name, ret);
>                       /* Continuing flushing all buffers */
>                       continue;
>               }
>       }
>  
>       /* Flush all buffers before stopping */
> -     ret = ustctl_sock_flush_buffer(app->key.sock, ua_sess->metadata->obj);
> +     ret = ustctl_sock_flush_buffer(app->sock, ua_sess->metadata->obj);
>       if (ret < 0) {
> -             ERR("UST app PID %d metadata flush failed with ret %d", 
> app->key.pid,
> +             ERR("UST app PID %d metadata flush failed with ret %d", 
> app->pid,
>                               ret);
>       }
>  
> @@ -2104,7 +2094,7 @@ int ust_app_destroy_trace(struct ltt_ust_session 
> *usess, struct ust_app *app)
>       struct lttng_ht_node_ulong *node;
>       int ret;
>  
> -     DBG("Destroy tracing for ust app pid %d", app->key.pid);
> +     DBG("Destroy tracing for ust app pid %d", app->pid);
>  
>       rcu_read_lock();
>  
> @@ -2125,12 +2115,12 @@ int ust_app_destroy_trace(struct ltt_ust_session 
> *usess, struct ust_app *app)
>       obj.shm_fd = -1;
>       obj.wait_fd = -1;
>       obj.memory_map_size = 0;
> -     ustctl_release_object(app->key.sock, &obj);
> +     ustctl_release_object(app->sock, &obj);
>  
> -     delete_ust_app_session(app->key.sock, ua_sess);
> +     delete_ust_app_session(app->sock, ua_sess);
>  
>       /* Quiescent wait after stopping trace */
> -     ustctl_wait_quiescent(app->key.sock);
> +     ustctl_wait_quiescent(app->sock);
>  
>  end:
>       rcu_read_unlock();
> @@ -2154,7 +2144,7 @@ int ust_app_start_trace_all(struct ltt_ust_session 
> *usess)
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               ret = ust_app_start_trace(usess, app);
>               if (ret < 0) {
>                       /* Continue to next apps even on error */
> @@ -2180,7 +2170,7 @@ int ust_app_stop_trace_all(struct ltt_ust_session 
> *usess)
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               ret = ust_app_stop_trace(usess, app);
>               if (ret < 0) {
>                       /* Continue to next apps even on error */
> @@ -2206,7 +2196,7 @@ int ust_app_destroy_trace_all(struct ltt_ust_session 
> *usess)
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               ret = ust_app_destroy_trace(usess, app);
>               if (ret < 0) {
>                       /* Continue to next apps even on error */
> @@ -2307,7 +2297,7 @@ void ust_app_global_update(struct ltt_ust_session 
> *usess, int sock)
>                       goto error;
>               }
>  
> -             DBG2("UST trace started for app pid %d", app->key.pid);
> +             DBG2("UST trace started for app pid %d", app->pid);
>       }
>  
>  error:
> @@ -2330,7 +2320,7 @@ int ust_app_add_ctx_channel_glb(struct ltt_ust_session 
> *usess,
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -2379,7 +2369,7 @@ int ust_app_add_ctx_event_glb(struct ltt_ust_session 
> *usess,
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -2567,7 +2557,7 @@ int ust_app_validate_version(int sock)
>       }
>  
>       DBG2("UST app PID %d is compatible with major version %d "
> -                     "(supporting <= %d)", app->key.pid, app->version.major,
> +                     "(supporting <= %d)", app->pid, app->version.major,
>                       UST_APP_MAJOR_VERSION);
>       app->compatible = 1;
>       rcu_read_unlock();
> @@ -2575,7 +2565,7 @@ int ust_app_validate_version(int sock)
>  
>  error:
>       DBG2("UST app PID %d is not compatible with major version %d "
> -                     "(supporting <= %d)", app->key.pid, app->version.major,
> +                     "(supporting <= %d)", app->pid, app->version.major,
>                       UST_APP_MAJOR_VERSION);
>       app->compatible = 0;
>       rcu_read_unlock();
> @@ -2593,7 +2583,7 @@ int ust_app_calibrate_glb(struct lttng_ust_calibrate 
> *calibrate)
>  
>       rcu_read_lock();
>  
> -     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, node.node) {
> +     cds_lfht_for_each_entry(ust_app_ht->ht, &iter.iter, app, pid_n.node) {
>               if (!app->compatible) {
>                       /*
>                        * TODO: In time, we should notice the caller of this 
> error by
> @@ -2602,7 +2592,7 @@ int ust_app_calibrate_glb(struct lttng_ust_calibrate 
> *calibrate)
>                       continue;
>               }
>  
> -             ret = ustctl_calibrate(app->key.sock, calibrate);
> +             ret = ustctl_calibrate(app->sock, calibrate);
>               if (ret < 0) {
>                       switch (ret) {
>                       case -ENOSYS:
> @@ -2612,7 +2602,7 @@ int ust_app_calibrate_glb(struct lttng_ust_calibrate 
> *calibrate)
>                       default:
>                               /* TODO: Report error to user */
>                               DBG2("Calibrate app PID %d returned with error 
> %d",
> -                                             app->key.pid, ret);
> +                                             app->pid, ret);
>                               break;
>                       }
>               }
> diff --git a/src/bin/lttng-sessiond/ust-app.h 
> b/src/bin/lttng-sessiond/ust-app.h
> index 906a6a2..8e98082 100644
> --- a/src/bin/lttng-sessiond/ust-app.h
> +++ b/src/bin/lttng-sessiond/ust-app.h
> @@ -45,17 +45,16 @@ struct ust_register_msg {
>  };
>  
>  /*
> - * Global applications HT used by the session daemon.
> + * Global applications HT used by the session daemon. This table is indexed 
> by
> + * PID using the pid_n node and pid value of an ust_app.
>   */
>  struct lttng_ht *ust_app_ht;
>  
> -struct lttng_ht *ust_app_sock_key_map;
> -
> -struct ust_app_key {
> -     pid_t pid;
> -     int sock;
> -     struct lttng_ht_node_ulong node;
> -};
> +/*
> + * Global applications HT used by the session daemon. This table is indexed 
> by
> + * socket using the sock_n node and sock value of an ust_app.
> + */
> +struct lttng_ht *ust_app_ht_by_sock;
>  
>  struct ust_app_ctx {
>       int handle;
> @@ -106,6 +105,8 @@ struct ust_app_session {
>   * and a linked list is kept of all running traceable app.
>   */
>  struct ust_app {
> +     int sock;
> +     pid_t pid;
>       pid_t ppid;
>       uid_t uid;           /* User ID that owns the apps */
>       gid_t gid;           /* Group ID that owns the apps */
> @@ -118,8 +119,8 @@ struct ust_app {
>       uint32_t v_minor;    /* Verion minor number */
>       char name[17];       /* Process name (short) */
>       struct lttng_ht *sessions;
> -     struct lttng_ht_node_ulong node;
> -     struct ust_app_key key;
> +     struct lttng_ht_node_ulong pid_n;
> +     struct lttng_ht_node_ulong sock_n;
>  };
>  
>  #ifdef HAVE_LIBLTTNG_UST_CTL
> diff --git a/src/common/hashtable/hashtable.h 
> b/src/common/hashtable/hashtable.h
> index d2d6979..f242e75 100644
> --- a/src/common/hashtable/hashtable.h
> +++ b/src/common/hashtable/hashtable.h
> @@ -72,8 +72,8 @@ extern void lttng_ht_add_unique_str(struct lttng_ht *ht,
>               struct lttng_ht_node_str *node);
>  extern void lttng_ht_add_unique_ulong(struct lttng_ht *ht,
>               struct lttng_ht_node_ulong *node);
> -struct lttng_ht_node_ulong *lttng_ht_add_replace_ulong(struct lttng_ht *ht,
> -             struct lttng_ht_node_ulong *node);
> +extern struct lttng_ht_node_ulong *lttng_ht_add_replace_ulong(
> +             struct lttng_ht *ht, struct lttng_ht_node_ulong *node);
>  
>  extern int lttng_ht_del(struct lttng_ht *ht, struct lttng_ht_iter *iter);
>  
> -- 
> 1.7.9.2
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com

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