Fix: application exit race with pthread cancel

Listener threads can be cancelled with ust lock held, which can hang the
following ust cleanup routine, because tracepoint probe unregister needs
to take the ust lock.

Fix this by disabling pthread cancellation for the entire duration of
the ust lock.

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 049667bf298d2122ffb904fc554b96744eb0083f..d48cc33627af5f4057060208e69b58afcdfc0b1f 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -111,8 +111,15 @@ static int lttng_ust_comm_should_quit;
 int ust_lock(void)
 {
        sigset_t sig_all_blocked, orig_mask;
-       int ret;
+       int ret, oldstate;
 
+       ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
+       if (ret) {
+               ERR("pthread_setcancelstate: %s", strerror(ret));
+       }
+       if (oldstate != PTHREAD_CANCEL_ENABLE) {
+               ERR("pthread_setcancelstate: unexpected oldstate");
+       }
        sigfillset(&sig_all_blocked);
        ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
        if (ret) {
@@ -140,8 +147,15 @@ int ust_lock(void)
 void ust_lock_nocheck(void)
 {
        sigset_t sig_all_blocked, orig_mask;
-       int ret;
+       int ret, oldstate;
 
+       ret = pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &oldstate);
+       if (ret) {
+               ERR("pthread_setcancelstate: %s", strerror(ret));
+       }
+       if (oldstate != PTHREAD_CANCEL_ENABLE) {
+               ERR("pthread_setcancelstate: unexpected oldstate");
+       }
        sigfillset(&sig_all_blocked);
        ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
        if (ret) {
@@ -161,7 +175,7 @@ void ust_lock_nocheck(void)
 void ust_unlock(void)
 {
        sigset_t sig_all_blocked, orig_mask;
-       int ret;
+       int ret, oldstate;
 
        sigfillset(&sig_all_blocked);
        ret = pthread_sigmask(SIG_SETMASK, &sig_all_blocked, &orig_mask);
@@ -174,6 +188,13 @@ void ust_unlock(void)
        if (ret) {
                ERR("pthread_sigmask: %s", strerror(ret));
        }
+       ret = pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, &oldstate);
+       if (ret) {
+               ERR("pthread_setcancelstate: %s", strerror(ret));
+       }
+       if (oldstate != PTHREAD_CANCEL_DISABLE) {
+               ERR("pthread_setcancelstate: unexpected oldstate");
+       }
 }
 
 /*