This patch is based on the below upstream commit.

It only includes relevant pthread_once bits.

commit 08192659bbeae149e7cb1f4c43547257f7099bb0

Author: Roland McGrath <roland@hack.frob.com>

Date:   Mon Jul 7 09:28:38 2014 -0700

    Get rid of nptl/sysdeps/ entirely!

diff --git a/nptl/pthread_once.c b/nptl/pthread_once.c

index ed1ea3498c397e5c..10c01d6023508e3c 100644

--- a/nptl/pthread_once.c

+++ b/nptl/pthread_once.c

@@ -1,6 +1,6 @@

-/* Copyright (C) 2002-2012 Free Software Foundation, Inc.

+/* Copyright (C) 2003-2014 Free Software Foundation, Inc.

    This file is part of the GNU C Library.

-   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

+   Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.

    The GNU C Library is free software; you can redistribute it and/or

    modify it under the terms of the GNU Lesser General Public

@@ -9,7 +9,7 @@

    The GNU C Library is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU

    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public

@@ -18,37 +18,114 @@

 #include "pthreadP.h"

 #include <lowlevellock.h>

+#include <atomic.h>

+unsigned long int __fork_generation attribute_hidden;

-static int once_lock = LLL_LOCK_INITIALIZER;

+static void

+clear_once_control (void *arg)

+{

+  pthread_once_t *once_control = (pthread_once_t *) arg;

+

+  /* Reset to the uninitialized state here.  We don't need a stronger memory

+     order because we do not need to make any other of our writes visible to

+     other threads that see this value: This function will be called if we

+     get interrupted (see __pthread_once), so all we need to relay to other

+     threads is the state being reset again.  */

+  *once_control = 0;

+  lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);

+}

+

+/* This is similar to a lock implementation, but we distinguish between three

+   states: not yet initialized (0), initialization finished (2), and

+   initialization in progress (__fork_generation | 1).  If in the first state,

+   threads will try to run the initialization by moving to the second state;

+   the first thread to do so via a CAS on once_control runs init_routine,

+   other threads block.

+   When forking the process, some threads can be interrupted during the second

+   state; they won't be present in the forked child, so we need to restart

+   initialization in the child.  To distinguish an in-progress initialization

+   from an interrupted initialization (in which case we need to reclaim the

+   lock), we look at the fork generation that's part of the second state: We

+   can reclaim iff it differs from the current fork generation.

+   XXX: This algorithm has an ABA issue on the fork generation: If an

+   initialization is interrupted, we then fork 2^30 times (30 bits of

+   once_control are used for the fork generation), and try to initialize

+   again, we can deadlock because we can't distinguish the in-progress and

+   interrupted cases anymore.  */

 int

 __pthread_once (once_control, init_routine)

      pthread_once_t *once_control;

      void (*init_routine) (void);

 {

-  /* XXX Depending on whether the LOCK_IN_ONCE_T is defined use a

-     global lock variable or one which is part of the pthread_once_t

-     object.  */

-  if (*once_control == PTHREAD_ONCE_INIT)

+  while (1)

     {

-      lll_lock (once_lock, LLL_PRIVATE);

+      int oldval, val, newval;

-      /* XXX This implementation is not complete.  It doesn't take

-	 cancelation and fork into account.  */

-      if (*once_control == PTHREAD_ONCE_INIT)

+      /* We need acquire memory order for this load because if the value

+         signals that initialization has finished, we need to be see any

+         data modifications done during initialization.  */

+      val = *once_control;

+      atomic_read_barrier();

+      do

 	{

-	  init_routine ();

+	  /* Check if the initialization has already been done.  */

+	  if (__glibc_likely ((val & 2) != 0))

+	    return 0;

+

+	  oldval = val;

+	  /* We try to set the state to in-progress and having the current

+	     fork generation.  We don't need atomic accesses for the fork

+	     generation because it's immutable in a particular process, and

+	     forked child processes start with a single thread that modified

+	     the generation.  */

+	  newval = __fork_generation | 1;

+	  /* We need acquire memory order here for the same reason as for the

+	     load from once_control above.  */

+	  val = atomic_compare_and_exchange_val_acq (once_control, newval,

+						     oldval);

+	}

+      while (__glibc_unlikely (val != oldval));

-	  *once_control = !PTHREAD_ONCE_INIT;

+      /* Check if another thread already runs the initializer.	*/

+      if ((oldval & 1) != 0)

+	{

+	  /* Check whether the initializer execution was interrupted by a

+	     fork.  We know that for both values, bit 0 is set and bit 1 is

+	     not.  */

+	  if (oldval == newval)

+	    {

+	      /* Same generation, some other thread was faster. Wait.  */

+	      lll_futex_wait (once_control, newval, LLL_PRIVATE);

+	      continue;

+	    }

 	}

-      lll_unlock (once_lock, LLL_PRIVATE);

+      /* This thread is the first here.  Do the initialization.

+	 Register a cleanup handler so that in case the thread gets

+	 interrupted the initialization can be restarted.  */

+      pthread_cleanup_push (clear_once_control, once_control);

+

+      init_routine ();

+

+      pthread_cleanup_pop (0);

+

+

+      /* Mark *once_control as having finished the initialization.  We need

+         release memory order here because we need to synchronize with other

+         threads that want to use the initialized data.  */

+      atomic_write_barrier();

+      *once_control = 2;

+

+      /* Wake up all other threads.  */

+      lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);

+      break;

     }

   return 0;

 }

-strong_alias (__pthread_once, pthread_once)

+weak_alias (__pthread_once, pthread_once)

 hidden_def (__pthread_once)

diff --git a/nptl/sysdeps/unix/sysv/linux/pthread_once.c b/nptl/sysdeps/unix/sysv/linux/pthread_once.c

deleted file mode 100644

index 2684b660958361d4..0000000000000000

--- a/nptl/sysdeps/unix/sysv/linux/pthread_once.c

+++ /dev/null

@@ -1,129 +0,0 @@

-/* Copyright (C) 2003-2014 Free Software Foundation, Inc.

-   This file is part of the GNU C Library.

-   Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.

-

-   The GNU C Library is free software; you can redistribute it and/or

-   modify it under the terms of the GNU Lesser General Public

-   License as published by the Free Software Foundation; either

-   version 2.1 of the License, or (at your option) any later version.

-

-   The GNU C Library is distributed in the hope that it will be useful,

-   but WITHOUT ANY WARRANTY; without even the implied warranty of

-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU

-   Lesser General Public License for more details.

-

-   You should have received a copy of the GNU Lesser General Public

-   License along with the GNU C Library; if not, see

-   <http://www.gnu.org/licenses/>.  */

-

-#include "pthreadP.h"

-#include <lowlevellock.h>

-#include <atomic.h>

-

-

-unsigned long int __fork_generation attribute_hidden;

-

-

-static void

-clear_once_control (void *arg)

-{

-  pthread_once_t *once_control = (pthread_once_t *) arg;

-

-  /* Reset to the uninitialized state here.  We don't need a stronger memory

-     order because we do not need to make any other of our writes visible to

-     other threads that see this value: This function will be called if we

-     get interrupted (see __pthread_once), so all we need to relay to other

-     threads is the state being reset again.  */

-  *once_control = 0;

-  lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);

-}

-

-

-/* This is similar to a lock implementation, but we distinguish between three

-   states: not yet initialized (0), initialization finished (2), and

-   initialization in progress (__fork_generation | 1).  If in the first state,

-   threads will try to run the initialization by moving to the second state;

-   the first thread to do so via a CAS on once_control runs init_routine,

-   other threads block.

-   When forking the process, some threads can be interrupted during the second

-   state; they won't be present in the forked child, so we need to restart

-   initialization in the child.  To distinguish an in-progress initialization

-   from an interrupted initialization (in which case we need to reclaim the

-   lock), we look at the fork generation that's part of the second state: We

-   can reclaim iff it differs from the current fork generation.

-   XXX: This algorithm has an ABA issue on the fork generation: If an

-   initialization is interrupted, we then fork 2^30 times (30 bits of

-   once_control are used for the fork generation), and try to initialize

-   again, we can deadlock because we can't distinguish the in-progress and

-   interrupted cases anymore.  */

-int

-__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))

-{

-  while (1)

-    {

-      int oldval, val, newval;

-

-      /* We need acquire memory order for this load because if the value

-         signals that initialization has finished, we need to be see any

-         data modifications done during initialization.  */

-      val = *once_control;

-      atomic_read_barrier();

-      do

-	{

-	  /* Check if the initialization has already been done.  */

-	  if (__glibc_likely ((val & 2) != 0))

-	    return 0;

-

-	  oldval = val;

-	  /* We try to set the state to in-progress and having the current

-	     fork generation.  We don't need atomic accesses for the fork

-	     generation because it's immutable in a particular process, and

-	     forked child processes start with a single thread that modified

-	     the generation.  */

-	  newval = __fork_generation | 1;

-	  /* We need acquire memory order here for the same reason as for the

-	     load from once_control above.  */

-	  val = atomic_compare_and_exchange_val_acq (once_control, newval,

-						     oldval);

-	}

-      while (__glibc_unlikely (val != oldval));

-

-      /* Check if another thread already runs the initializer.	*/

-      if ((oldval & 1) != 0)

-	{

-	  /* Check whether the initializer execution was interrupted by a

-	     fork.  We know that for both values, bit 0 is set and bit 1 is

-	     not.  */

-	  if (oldval == newval)

-	    {

-	      /* Same generation, some other thread was faster. Wait.  */

-	      lll_futex_wait (once_control, newval, LLL_PRIVATE);

-	      continue;

-	    }

-	}

-

-      /* This thread is the first here.  Do the initialization.

-	 Register a cleanup handler so that in case the thread gets

-	 interrupted the initialization can be restarted.  */

-      pthread_cleanup_push (clear_once_control, once_control);

-

-      init_routine ();

-

-      pthread_cleanup_pop (0);

-

-

-      /* Mark *once_control as having finished the initialization.  We need

-         release memory order here because we need to synchronize with other

-         threads that want to use the initialized data.  */

-      atomic_write_barrier();

-      *once_control = 2;

-

-      /* Wake up all other threads.  */

-      lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);

-      break;

-    }

-

-  return 0;

-}

-weak_alias (__pthread_once, pthread_once)

-hidden_def (__pthread_once)