Linux: Move timer helper routines from librt to libc

This adds several temporary GLIBC_PRIVATE exports.  The symbol names
are changed so that they all start with __timer_.

It is now possible to invoke the fork handler directly, so
pthread_atfork is no longer necessary.  The associated error cannot
happen anymore, and cancellation handling can be removed from
the helper thread routine.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

sysdeps/nptl/Makefile

@@ -17,7 +17,7 @@
 # <https://www.gnu.org/licenses/>.
 
 ifeq ($(subdir),rt)
-librt-sysdep_routines += timer_routines
+sysdep_routines += timer_routines
 
 tests += tst-mqueue8x
 CFLAGS-tst-mqueue8x.c += -fexceptions

sysdeps/nptl/fork.h

@@ -20,6 +20,7 @@
 #define _FORK_H
 
 #include <assert.h>
+#include <kernel-posix-timers.h>
 #include <ldsodefs.h>
 #include <list.h>
 #include <mqueue.h>
@@ -44,6 +45,7 @@ fork_system_setup_after_fork (void)
   __default_pthread_attr_lock = LLL_LOCK_INITIALIZER;
 
   call_function_static_weak (__mq_notify_fork_subprocess);
+  call_function_static_weak (__timer_fork_subprocess);
 }
 
 /* In case of a fork() call the memory allocation in the child will be

sysdeps/unix/sysv/linux/Versions

@@ -282,6 +282,11 @@ libc {
     __pread64_nocancel;
     __close_nocancel;
     __sigtimedwait;
+    __timer_active_sigev_thread;
+    __timer_active_sigev_thread_lock;
+    __timer_helper_once;
+    __timer_helper_tid;
+    __timer_start_helper_thread;
     # functions used by nscd
     __netlink_assert_response;
   }

sysdeps/unix/sysv/linux/kernel-posix-timers.h

@@ -26,19 +26,27 @@
 extern int __no_posix_timers attribute_hidden;
 
 /* Callback to start helper thread.  */
-extern void __start_helper_thread (void) attribute_hidden;
+extern void __timer_start_helper_thread (void);
+libc_hidden_proto (__timer_start_helper_thread)
 
 /* Control variable for helper thread creation.  */
-extern pthread_once_t __helper_once attribute_hidden;
+extern pthread_once_t __timer_helper_once;
+libc_hidden_proto (__timer_helper_once)
+
+/* Called from fork so that the new subprocess re-creates the
+   notification thread if necessary.  */
+void __timer_fork_subprocess (void) attribute_hidden;
 
 /* TID of the helper thread.  */
-extern pid_t __helper_tid attribute_hidden;
+extern pid_t __timer_helper_tid;
+libc_hidden_proto (__timer_helper_tid)
 
 /* List of active SIGEV_THREAD timers.  */
-extern struct timer *__active_timer_sigev_thread attribute_hidden;
-/* Lock for the __active_timer_sigev_thread.  */
-extern pthread_mutex_t __active_timer_sigev_thread_lock attribute_hidden;
-
+extern struct timer *__timer_active_sigev_thread;
+libc_hidden_proto (__timer_active_sigev_thread)
+/* Lock for __timer_active_sigev_thread.  */
+extern pthread_mutex_t __timer_active_sigev_thread_lock;
+libc_hidden_proto (__timer_active_sigev_thread_lock)
 
 /* Type of timers in the kernel.  */
 typedef int kernel_timer_t;

sysdeps/unix/sysv/linux/timer_create.c

@@ -74,8 +74,8 @@ timer_create (clockid_t clock_id, struct sigevent *evp, timer_t *timerid)
     else
       {
 	/* Create the helper thread.  */
-	pthread_once (&__helper_once, __start_helper_thread);
-	if (__helper_tid == 0)
+	pthread_once (&__timer_helper_once, __timer_start_helper_thread);
+	if (__timer_helper_tid == 0)
 	  {
 	    /* No resources to start the helper thread.  */
 	    __set_errno (EAGAIN);
@@ -118,7 +118,7 @@ timer_create (clockid_t clock_id, struct sigevent *evp, timer_t *timerid)
 	  { .sigev_value.sival_ptr = newp,
 	    .sigev_signo = SIGTIMER,
 	    .sigev_notify = SIGEV_SIGNAL | SIGEV_THREAD_ID,
-	    ._sigev_un = { ._pad = { [0] = __helper_tid } } };
+	    ._sigev_un = { ._pad = { [0] = __timer_helper_tid } } };
 
 	/* Create the timer.  */
 	int res;
@@ -132,10 +132,10 @@ timer_create (clockid_t clock_id, struct sigevent *evp, timer_t *timerid)
 	  }
 
 	/* Add to the queue of active timers with thread delivery.  */
-	pthread_mutex_lock (&__active_timer_sigev_thread_lock);
-	newp->next = __active_timer_sigev_thread;
-	__active_timer_sigev_thread = newp;
-	pthread_mutex_unlock (&__active_timer_sigev_thread_lock);
+	pthread_mutex_lock (&__timer_active_sigev_thread_lock);
+	newp->next = __timer_active_sigev_thread;
+	__timer_active_sigev_thread = newp;
+	pthread_mutex_unlock (&__timer_active_sigev_thread_lock);
 
 	*timerid = timer_to_timerid (newp);
       }

sysdeps/unix/sysv/linux/timer_delete.c

@@ -42,12 +42,12 @@ timer_delete (timer_t timerid)
 	  struct timer *kt = timerid_to_timer (timerid);
 
 	  /* Remove the timer from the list.  */
-	  pthread_mutex_lock (&__active_timer_sigev_thread_lock);
-	  if (__active_timer_sigev_thread == kt)
-	    __active_timer_sigev_thread = kt->next;
+	  pthread_mutex_lock (&__timer_active_sigev_thread_lock);
+	  if (__timer_active_sigev_thread == kt)
+	    __timer_active_sigev_thread = kt->next;
 	  else
 	    {
-	      struct timer *prevp = __active_timer_sigev_thread;
+	      struct timer *prevp = __timer_active_sigev_thread;
 	      while (prevp->next != NULL)
 		if (prevp->next == kt)
 		  {
@@ -57,7 +57,7 @@ timer_delete (timer_t timerid)
 		else
 		  prevp = prevp->next;
 	    }
-	  pthread_mutex_unlock (&__active_timer_sigev_thread_lock);
+	  pthread_mutex_unlock (&__timer_active_sigev_thread_lock);
 
 	  free (kt);
 	}

sysdeps/unix/sysv/linux/timer_routines.c

@@ -26,10 +26,13 @@
 
 
 /* List of active SIGEV_THREAD timers.  */
-struct timer *__active_timer_sigev_thread;
-/* Lock for the __active_timer_sigev_thread.  */
-pthread_mutex_t __active_timer_sigev_thread_lock = PTHREAD_MUTEX_INITIALIZER;
+struct timer *__timer_active_sigev_thread __attribute__ ((nocommon));
+libc_hidden_data_def (__timer_active_sigev_thread)
 
+/* Lock for _timer_active_sigev_thread.  */
+pthread_mutex_t __timer_active_sigev_thread_lock __attribute__ ((nocommon))
+  = PTHREAD_MUTEX_INITIALIZER;
+libc_hidden_data_def (__timer_active_sigev_thread_lock)
 
 struct thread_start_data
 {
@@ -59,7 +62,7 @@ timer_sigev_thread (void *arg)
 
 
 /* Helper function to support starting threads for SIGEV_THREAD.  */
-static void *
+static _Noreturn void *
 timer_helper_thread (void *arg)
 {
   /* Endless loop of waiting for signals.  The loop is only ended when
@@ -68,16 +71,16 @@ timer_helper_thread (void *arg)
     {
       siginfo_t si;
 
-      while (sigwaitinfo (&sigtimer_set, &si) < 0);
+      while (__sigwaitinfo (&sigtimer_set, &si) < 0);
       if (si.si_code == SI_TIMER)
 	{
 	  struct timer *tk = (struct timer *) si.si_ptr;
 
 	  /* Check the timer is still used and will not go away
 	     while we are reading the values here.  */
-	  pthread_mutex_lock (&__active_timer_sigev_thread_lock);
+	  __pthread_mutex_lock (&__timer_active_sigev_thread_lock);
 
-	  struct timer *runp = __active_timer_sigev_thread;
+	  struct timer *runp = __timer_active_sigev_thread;
 	  while (runp != NULL)
 	    if (runp == tk)
 	      break;
@@ -96,45 +99,44 @@ timer_helper_thread (void *arg)
 		  td->sival = tk->sival;
 
 		  pthread_t th;
-		  pthread_create (&th, &tk->attr, timer_sigev_thread, td);
+		  __pthread_create (&th, &tk->attr, timer_sigev_thread, td);
 		}
 	    }
 
-	  pthread_mutex_unlock (&__active_timer_sigev_thread_lock);
+	  __pthread_mutex_unlock (&__timer_active_sigev_thread_lock);
 	}
-      else if (si.si_code == SI_TKILL)
-	/* The thread is canceled.  */
-	pthread_exit (NULL);
     }
 }
 
 
 /* Control variable for helper thread creation.  */
-pthread_once_t __helper_once attribute_hidden;
+pthread_once_t __timer_helper_once __attribute__ ((nocommon))
+  = PTHREAD_ONCE_INIT;
+libc_hidden_data_def (__timer_helper_once)
 
 
 /* TID of the helper thread.  */
-pid_t __helper_tid attribute_hidden;
+pid_t __timer_helper_tid __attribute__ ((nocommon));
+libc_hidden_data_def (__timer_helper_tid)
 
 
 /* Reset variables so that after a fork a new helper thread gets started.  */
-static void
-reset_helper_control (void)
+void
+__timer_fork_subprocess (void)
 {
-  __helper_once = PTHREAD_ONCE_INIT;
-  __helper_tid = 0;
+  __timer_helper_once = PTHREAD_ONCE_INIT;
+  __timer_helper_tid = 0;
 }
 
 
 void
-attribute_hidden
-__start_helper_thread (void)
+__timer_start_helper_thread (void)
 {
   /* The helper thread needs only very little resources
      and should go away automatically when canceled.  */
   pthread_attr_t attr;
-  (void) pthread_attr_init (&attr);
-  (void) pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr));
+  __pthread_attr_init (&attr);
+  __pthread_attr_setstacksize (&attr, __pthread_get_minstack (&attr));
 
   /* Block all signals in the helper thread but SIGSETXID.  */
   sigset_t ss;
@@ -143,21 +145,18 @@ __start_helper_thread (void)
   int res = __pthread_attr_setsigmask_internal (&attr, &ss);
   if (res != 0)
     {
-      pthread_attr_destroy (&attr);
+      __pthread_attr_destroy (&attr);
       return;
     }
 
   /* Create the helper thread for this timer.  */
   pthread_t th;
-  res = pthread_create (&th, &attr, timer_helper_thread, NULL);
+  res = __pthread_create (&th, &attr, timer_helper_thread, NULL);
   if (res == 0)
     /* We managed to start the helper thread.  */
-    __helper_tid = ((struct pthread *) th)->tid;
+    __timer_helper_tid = ((struct pthread *) th)->tid;
 
   /* No need for the attribute anymore.  */
-  (void) pthread_attr_destroy (&attr);
-
-  /* We have to make sure that after fork()ing a new helper thread can
-     be created.  */
-  pthread_atfork (NULL, NULL, reset_helper_control);
+  __pthread_attr_destroy (&attr);
 }
+libc_hidden_def (__timer_start_helper_thread)