Fix: reset procname on fork in child process

[deliverable/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 32ba3c1d49e2ba7bbec27ffb2f0d3f502d168653..b61833155425988d261e9e584247e3b76ebf9c90 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -27,6 +27,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <dlfcn.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <errno.h>
@@ -59,6 +60,9 @@
 #include "../libringbuffer/getcpu.h"
 #include "getenv.h"
 
+/* Concatenate lttng ust shared library name with its major version number. */
+#define LTTNG_UST_LIB_SO_NAME "liblttng-ust.so." LTTNG_UST_LIBRARY_VERSION_MAJOR
+
 /*
  * Has lttng ust comm constructor been called ?
  */
@@ -1396,6 +1400,10 @@ restart:
                prev_connect_failed = 0;
        }
 
+       if (ust_lock()) {
+               goto quit;
+       }
+
        if (sock_info->socket != -1) {
                /* FD tracker is updated by ustcomm_close_unix_sock() */
                ret = ustcomm_close_unix_sock(sock_info->socket);
@@ -1415,9 +1423,6 @@ restart:
                sock_info->notify_socket = -1;
        }
 
-       if (ust_lock()) {
-               goto quit;
-       }
 
        /*
         * Register. We need to perform both connect and sending
@@ -1684,6 +1689,7 @@ void __attribute__((constructor)) lttng_ust_init(void)
        pthread_attr_t thread_attr;
        int timeout_mode;
        int ret;
+       void *handle;
 
        if (uatomic_xchg(&initialized, 1) == 1)
                return;
@@ -1697,6 +1703,26 @@ void __attribute__((constructor)) lttng_ust_init(void)
 
        lttng_ust_loaded = 1;
 
+       /*
+        * We need to ensure that the liblttng-ust library is not unloaded to avoid
+        * the unloading of code used by the ust_listener_threads as we can not
+        * reliably know when they exited. To do that, manually load
+        * liblttng-ust.so to increment the dynamic loader's internal refcount for
+        * this library so it never becomes zero, thus never gets unloaded from the
+        * address space of the process. Since we are already running in the
+        * constructor of the LTTNG_UST_LIB_SO_NAME library, calling dlopen will
+        * simply increment the refcount and no additionnal work is needed by the
+        * dynamic loader as the shared library is already loaded in the address
+        * space. As a safe guard, we use the RTLD_NODELETE flag to prevent
+        * unloading of the UST library if its refcount becomes zero (which should
+        * never happen). Do the return value check but discard the handle at the
+        * end of the function as it's not needed.
+        */
+       handle = dlopen(LTTNG_UST_LIB_SO_NAME, RTLD_LAZY | RTLD_NODELETE);
+       if (!handle) {
+               ERR("dlopen of liblttng-ust shared library (%s).", LTTNG_UST_LIB_SO_NAME);
+       }
+
        /*
         * We want precise control over the order in which we construct
         * our sub-libraries vs starting to receive commands from
@@ -1985,7 +2011,9 @@ void ust_after_fork_child(sigset_t *restore_sigset)
 {
        if (URCU_TLS(lttng_ust_nest_count))
                return;
+       lttng_context_vpid_reset();
        lttng_context_vtid_reset();
+       lttng_context_procname_reset();
        DBG("process %d", getpid());
        /* Release urcu mutexes */
        rcu_bp_after_fork_child();