sessiond: use epoll()/poll() instead of select()

The select(2) system call is an ancient ABI limited to processes
containing at most FD_SETSIZE file descriptors overall (typically
1024).

This select call will fail if the target file descriptor is above
FD_SETSIZE in a session daemon containing many file descriptors.
This is unlikely to happen in normal use given than
sessiond_init_thread_quit_pipe() is called early by main(). Odd
scenarios could trigger this, for instance if the parent process leaves
a large number of file descriptors open, or if a library which
allocates file descriptors is LD_PRELOADed with the sessiond.

Never use select, use the lttng epoll/poll wrapper instead.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng-sessiond/lttng-sessiond.h b/src/bin/lttng-sessiond/lttng-sessiond.h
index 1dc6fade8fac43a54d2a4c17687f8d6e0047bc54..1cd9eeab6b692ddd4c25111b812962e03b403a18 100644 (file)
--- a/src/bin/lttng-sessiond/lttng-sessiond.h
+++ b/src/bin/lttng-sessiond/lttng-sessiond.h
@@ -164,7 +164,7 @@ extern struct consumer_data kconsumer_data;
 
 int sessiond_init_thread_quit_pipe(void);
 int sessiond_check_thread_quit_pipe(int fd, uint32_t events);
-int sessiond_wait_for_quit_pipe(unsigned int timeout_us);
+int sessiond_wait_for_quit_pipe(int timeout_ms);
 int sessiond_notify_quit_pipe(void);
 void sessiond_close_quit_pipe(void);
 

diff --git a/src/bin/lttng-sessiond/main.c b/src/bin/lttng-sessiond/main.c
index a29417af59e7aeb7a90513cc5346f21db82f6346..f698fae4c634be7b3445d9dc0e6d29253352f549 100644 (file)
--- a/src/bin/lttng-sessiond/main.c
+++ b/src/bin/lttng-sessiond/main.c
@@ -1841,7 +1841,7 @@ int main(int argc, char **argv)
         */
 
        /* Initiate teardown once activity occurs on the quit pipe. */
-       sessiond_wait_for_quit_pipe(-1U);
+       sessiond_wait_for_quit_pipe(-1);
 
 stop_threads:
        /*

diff --git a/src/bin/lttng-sessiond/thread-utils.c b/src/bin/lttng-sessiond/thread-utils.c
index 16ae9d69204a971b07ac6d2857a148df87d983bd..60d4c276224edf402c3a30af2738990631958c7a 100644 (file)
--- a/src/bin/lttng-sessiond/thread-utils.c
+++ b/src/bin/lttng-sessiond/thread-utils.c
@@ -73,41 +73,38 @@ int sessiond_check_thread_quit_pipe(int fd, uint32_t events)
  * Returns 1 if the caller should quit, 0 if the timeout was reached, and
  * -1 if an error was encountered.
  */
-int sessiond_wait_for_quit_pipe(unsigned int timeout_us)
+int sessiond_wait_for_quit_pipe(int timeout_ms)
 {
        int ret;
-       fd_set read_fds;
-       struct timeval timeout;
-
-       FD_ZERO(&read_fds);
-       FD_SET(thread_quit_pipe[0], &read_fds);
-       memset(&timeout, 0, sizeof(timeout));
-       timeout.tv_sec = timeout_us / USEC_PER_SEC;
-       timeout.tv_usec = timeout_us % USEC_PER_SEC;
-
-       while (true) {
-               ret = select(thread_quit_pipe[0] + 1, &read_fds, NULL, NULL,
-                               timeout_us != -1U ? &timeout : NULL);
-               if (ret < 0 && errno == EINTR) {
-                       /* Retry on interrupt. */
-                       continue;
-               } else {
-                       break;
-               }
-       }
+       struct lttng_poll_event events;
 
+       ret = lttng_poll_create(&events, 1, LTTNG_CLOEXEC);
+       if (ret < 0) {
+               PERROR("Failed to initialize poll/epoll set");
+               ret = -1;
+               goto end;
+       }
+       ret = lttng_poll_add(&events, thread_quit_pipe[0], LPOLLIN | LPOLLERR);
+       if (ret < 0) {
+               PERROR("Failed to add file descriptor to poll/epoll set");
+               ret = -1;
+               goto end_clean_poll;
+       }
+       ret = lttng_poll_wait(&events, timeout_ms);
        if (ret > 0) {
                /* Should quit. */
                ret = 1;
        } else if (ret < 0 && errno != EINTR) {
                /* Unknown error. */
-               PERROR("Failed to select() thread quit pipe");
+               PERROR("Failed to epoll()/poll() thread quit pipe");
                ret = -1;
        } else {
                /* Timeout reached. */
                ret = 0;
        }
-
+end_clean_poll:
+       lttng_poll_clean(&events);
+end:
        return ret;
 }