commands: remove mutex from state client list

I was thinking about the locking here yesterday and it dawned on me that we
actually don't need this at all:
- possible contention between traversing list to send states to state clients
  and adding new state clients to the list:
  It is the command handler that adds new state clients to the state client
  list. The command handler and the code that actually sends out the container
  states run in the same process so there's not contention and thus no locking
  needed.
- adding state clients to the list from multiple threads:
  The command handler itself is single-threaded so only one thread's request can
  be served at the same time so no locking is needed.
- sending out the state to state clients via the command handler itself:
  The state client also adds and removes state clients from the state client
  list so there's no locking needed.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/src/lxc/commands.c b/src/lxc/commands.c
index 3062ec11ec238fceb15ecca0c27938545f0e4691..2246b0c4a4397b139f8c431d9918cdc9ab05b4fa 100644 (file)
--- a/src/lxc/commands.c
+++ b/src/lxc/commands.c
@@ -1149,7 +1149,6 @@ static void lxc_cmd_fd_cleanup(int fd, struct lxc_handler *handler,
                return;
        }
 
-       process_lock();
        lxc_list_for_each_safe(cur, &handler->conf->state_clients, next) {
                client = cur->elem;
                if (client->clientfd != fd)
@@ -1165,7 +1164,6 @@ static void lxc_cmd_fd_cleanup(int fd, struct lxc_handler *handler,
                 */
                break;
        }
-       process_unlock();
 }
 
 static int lxc_cmd_handler(int fd, uint32_t events, void *data,

diff --git a/src/lxc/commands_utils.c b/src/lxc/commands_utils.c
index 12b13170789bbf2bdf5e6e9b3dcce5176793e199..3a96b42dd825e3dffd1ae858bd846bcb0983b44c 100644 (file)
--- a/src/lxc/commands_utils.c
+++ b/src/lxc/commands_utils.c
@@ -211,14 +211,11 @@ int lxc_add_state_client(int state_client_fd, struct lxc_handler *handler,
                return -ENOMEM;
        }
 
-       process_lock();
        state = handler->state;
        if (states[state] != 1) {
                lxc_list_add_elem(tmplist, newclient);
                lxc_list_add_tail(&handler->conf->state_clients, tmplist);
-               process_unlock();
        } else {
-               process_unlock();
                free(newclient);
                free(tmplist);
                return state;

diff --git a/src/lxc/start.c b/src/lxc/start.c
index 1279635d6e269913a313fef13c41473a1f8f4141..5438ebda09eeca3b5dd6649760a5aa7070f16e6e 100644 (file)
--- a/src/lxc/start.c
+++ b/src/lxc/start.c
@@ -390,7 +390,6 @@ int lxc_serve_state_clients(const char *name, struct lxc_handler *handler,
        struct lxc_state_client *client;
        struct lxc_msg msg = {.type = lxc_msg_state, .value = state};
 
-       process_lock();
        if (state == THAWED)
                handler->state = RUNNING;
        else
@@ -400,7 +399,6 @@ int lxc_serve_state_clients(const char *name, struct lxc_handler *handler,
 
        if (lxc_list_empty(&handler->conf->state_clients)) {
                TRACE("No state clients registered");
-               process_unlock();
                return 0;
        }
 
@@ -437,7 +435,6 @@ int lxc_serve_state_clients(const char *name, struct lxc_handler *handler,
                free(cur->elem);
                free(cur);
        }
-       process_unlock();
 
        return 0;
 }