fix: Handle sys_futex with async cancel, add missing pthread_join

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

diff --git a/liblttng-ust/lttng-ust-comm.c b/liblttng-ust/lttng-ust-comm.c
index dda4743fc240cf7c2dc7f71e15846a8ec2a691ca..f41863628c9a097d8394eaa35a2ce2e834ee4e12 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, int exiting)
+void cleanup_sock_info(struct sock_info *sock_info)
 {
        int ret;
 
@@ -402,18 +402,7 @@ void cleanup_sock_info(struct sock_info *sock_info, int exiting)
                sock_info->root_handle = -1;
        }
        sock_info->constructor_sem_posted = 0;
-       /*
-        * When called from process exit, we allow this memory map to be
-        * released by the OS at exit(), because removing it prior to
-        * this can cause a segmentation fault when using the
-        * futex_async timer-based fallback. And we cannot join those
-        * threads because sys_futex does not react to the cancellation
-        * request.
-        *
-        * So we actually _do_ release it only after a fork, since all
-        * threads have vanished anyway.
-        */
-       if (!exiting && sock_info->wait_shm_mmap) {
+       if (sock_info->wait_shm_mmap) {
                ret = munmap(sock_info->wait_shm_mmap, sysconf(_SC_PAGE_SIZE));
                if (ret) {
                        ERR("Error unmapping wait shm");
@@ -589,7 +578,7 @@ error:
 static
 void wait_for_sessiond(struct sock_info *sock_info)
 {
-       int ret;
+       int ret, oldtype;
 
        ust_lock();
        if (lttng_ust_comm_should_quit) {
@@ -606,6 +595,14 @@ 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,
@@ -624,6 +621,10 @@ void wait_for_sessiond(struct sock_info *sock_info)
                        }
                }
        }
+       ret = pthread_setcanceltype(oldtype, &oldtype);
+       if (ret) {
+               ERR("Error setting thread cancel type");
+       }
        return;
 
 quit:
@@ -887,9 +888,9 @@ void __attribute__((constructor)) lttng_ust_init(void)
 static
 void lttng_ust_cleanup(int exiting)
 {
-       cleanup_sock_info(&global_apps, exiting);
+       cleanup_sock_info(&global_apps);
        if (local_apps.allowed) {
-               cleanup_sock_info(&local_apps, exiting);
+               cleanup_sock_info(&local_apps);
        }
        lttng_ust_abi_exit();
        lttng_ust_events_exit();
@@ -924,6 +925,7 @@ void __attribute__((destructor)) lttng_ust_exit(void)
        lttng_ust_comm_should_quit = 1;
        ust_unlock();
 
+       /* cancel threads */
        ret = pthread_cancel(global_apps.ust_listener);
        if (ret) {
                ERR("Error cancelling global ust listener thread");
@@ -934,10 +936,17 @@ void __attribute__((destructor)) lttng_ust_exit(void)
                        ERR("Error cancelling local ust listener thread");
                }
        }
-       /*
-        * We cannot join the threads because they might be waiting on
-        * sys_futex. Simply let the OS exit() clean up those threads.
-        */
+       /* 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");
+               }
+       }
        lttng_ust_cleanup(1);
 }