fix: on exit, leave thread/mmap reclaim to OS

[lttng-ust.git] / liblttng-ust / lttng-ust-comm.c

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index f41863628c9a097d8394eaa35a2ce2e834ee4e12..86cce18d57fe658588db907ed8016f39e95f975f 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -383,7 +383,7 @@ error:
 }
 
 static
-void cleanup_sock_info(struct sock_info *sock_info)
+void cleanup_sock_info(struct sock_info *sock_info, int exiting)
 {
        int ret;
 
@@ -402,7 +402,13 @@ void cleanup_sock_info(struct sock_info *sock_info)
                sock_info->root_handle = -1;
        }
        sock_info->constructor_sem_posted = 0;
-       if (sock_info->wait_shm_mmap) {
+       /*
+        * wait_shm_mmap is used by listener threads outside of the
+        * ust lock, so we cannot tear it down ourselves, because we
+        * cannot join on these threads. Leave this task to the OS
+        * process exit.
+        */
+       if (!exiting && sock_info->wait_shm_mmap) {
                ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
                if (ret) {
                        ERR("Error unmapping wait shm");
@@ -578,7 +584,7 @@ error:
 static
 void wait_for_sessiond(struct sock_info *sock_info)
 {
-       int ret, oldtype;
+       int ret;
 
        ust_lock();
        if (lttng_ust_comm_should_quit) {
@@ -595,14 +601,6 @@ void wait_for_sessiond(struct sock_info *sock_info)
        ust_unlock();
 
        DBG("Waiting for %s apps sessiond", sock_info->name);
-       /*
-        * sys_futex does not honor pthread cancel requests. Set to
-        * async.
-        */
-       ret = pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, &oldtype);
-       if (ret) {
-               ERR("Error setting thread cancel type");
-       }
        /* Wait for futex wakeup */
        if (uatomic_read((int32_t *) sock_info->wait_shm_mmap) == 0) {
                ret = futex_async((int32_t *) sock_info->wait_shm_mmap,
@@ -621,10 +619,6 @@ void wait_for_sessiond(struct sock_info *sock_info)
                        }
                }
        }
-       ret = pthread_setcanceltype(oldtype, &oldtype);
-       if (ret) {
-               ERR("Error setting thread cancel type");
-       }
        return;
 
 quit:
@@ -888,10 +882,17 @@ void __attribute__((constructor)) lttng_ust_init(void)
 static
 void lttng_ust_cleanup(int exiting)
 {
-       cleanup_sock_info(&global_apps);
+       cleanup_sock_info(&global_apps, exiting);
        if (local_apps.allowed) {
-               cleanup_sock_info(&local_apps);
+               cleanup_sock_info(&local_apps, exiting);
        }
+       /*
+        * The teardown in this function all affect data structures
+        * accessed under the UST lock by the listener thread. This
+        * lock, along with the lttng_ust_comm_should_quit flag, ensure
+        * that none of these threads are accessing this data at this
+        * point.
+        */
        lttng_ust_abi_exit();
        lttng_ust_events_exit();
        ltt_ring_buffer_client_discard_exit();
@@ -936,17 +937,14 @@ void __attribute__((destructor)) lttng_ust_exit(void)
                        ERR("Error cancelling local ust listener thread");
                }
        }
-       /* join threads */
-       ret = pthread_join(global_apps.ust_listener, NULL);
-       if (ret) {
-               ERR("Error joining global ust listener thread");
-       }
-       if (local_apps.allowed) {
-               ret = pthread_join(local_apps.ust_listener, NULL);
-               if (ret) {
-                       ERR("Error joining local ust listener thread");
-               }
-       }
+       /*
+        * Do NOT join threads: use of sys_futex makes it impossible to
+        * join the threads without using async-cancel, but async-cancel
+        * is delivered by a signal, which could hit the target thread
+        * anywhere in its code path, including while the ust_lock() is
+        * held, causing a deadlock for the other thread. Let the OS
+        * cleanup the threads if there are stalled in a syscall.
+        */
        lttng_ust_cleanup(1);
 }