Fix: application SIGBUS when starting in parallel with sessiond

[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 1c7584ddd51e84ed3d1d55015467101791bd4657..e8c85304e798b446ecf17110cc9e3fd70464527f 100644 (file)
--- a/liblttng-ust/lttng-ust-comm.c
+++ b/liblttng-ust/lttng-ust-comm.c
@@ -689,6 +689,30 @@ int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
         */
        wait_shm_fd = shm_open(sock_info->wait_shm_path, O_RDONLY, 0);
        if (wait_shm_fd >= 0) {
+               int32_t tmp_read;
+               ssize_t len;
+               size_t bytes_read = 0;
+
+               /*
+                * Try to read the fd. If unable to do so, try opening
+                * it in write mode.
+                */
+               do {
+                       len = read(wait_shm_fd,
+                               &((char *) &tmp_read)[bytes_read],
+                               sizeof(tmp_read) - bytes_read);
+                       if (len > 0) {
+                               bytes_read += len;
+                       }
+               } while ((len < 0 && errno == EINTR)
+                       || (len > 0 && bytes_read < sizeof(tmp_read)));
+               if (bytes_read != sizeof(tmp_read)) {
+                       ret = close(wait_shm_fd);
+                       if (ret) {
+                               ERR("close wait_shm_fd");
+                       }
+                       goto open_write;
+               }
                goto end;
        } else if (wait_shm_fd < 0 && errno != ENOENT) {
                /*
@@ -699,9 +723,11 @@ int get_wait_shm(struct sock_info *sock_info, size_t mmap_size)
                ERR("Error opening shm %s", sock_info->wait_shm_path);
                goto end;
        }
+
+open_write:
        /*
-        * If the open failed because the file did not exist, try
-        * creating it ourself.
+        * If the open failed because the file did not exist, or because
+        * the file was not truncated yet, try creating it ourself.
         */
        URCU_TLS(lttng_ust_nest_count)++;
        pid = fork();