[3/5] nptl: Replace non cancellable pause/nanosleep with futex
diff mbox series

Message ID 20191030200052.497-3-adhemerval.zanella@linaro.org
State New
Headers show
Series
  • [1/5] Consolidate futex-internal.h
Related show

Commit Message

Adhemerval Zanella Oct. 30, 2019, 8 p.m. UTC
To help y2038 work avoid duplicate all the logic of nanosleep on
non cancellable version, the patch replaces it with a new futex
operation, lll_timedwait.  The changes are:

  - Add a expected value for __lll_clocklock_wait, so it can be used
    to wait for generic values.

  - Remove its internal atomic operation and move the logic to
    __lll_clocklock.  It makes __lll_clocklock_wait even more generic
    and __lll_clocklock slight faster on fast-path (since it won't
    require a function call anymore).

  - Add lll_timedwait, which uses __lll_clocklock_wait, to replace both
    __pause_nocancel and __nanosleep_nocancel.

It also allows remove the sparc32 __lll_clocklock_wait implementation
(since it is similar to the generic one).

Checked on x86_64-linux-gnu, sparcv9-linux-gnu, and i686-linux-gnu.
---
 nptl/lll_timedlock_wait.c                    | 35 ++++++++--------
 nptl/pthread_mutex_lock.c                    |  3 +-
 nptl/pthread_mutex_timedlock.c               | 20 ++--------
 sysdeps/nptl/lowlevellock.h                  | 15 ++++++-
 sysdeps/sparc/sparc32/lll_timedlock_wait.c   |  1 -
 sysdeps/sparc/sparc32/lowlevellock.c         | 42 --------------------
 sysdeps/unix/sysv/linux/sparc/lowlevellock.h | 22 +++++++++-
 7 files changed, 56 insertions(+), 82 deletions(-)
 delete mode 100644 sysdeps/sparc/sparc32/lll_timedlock_wait.c

Comments

Carlos O'Donell Oct. 30, 2019, 9:08 p.m. UTC | #1
On 10/30/19 4:00 PM, Adhemerval Zanella wrote:
> To help y2038 work avoid duplicate all the logic of nanosleep on
> non cancellable version, the patch replaces it with a new futex
> operation, lll_timedwait.  The changes are:

OK for master.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

>   - Add a expected value for __lll_clocklock_wait, so it can be used
>     to wait for generic values.

OK.

>   - Remove its internal atomic operation and move the logic to
>     __lll_clocklock.  It makes __lll_clocklock_wait even more generic
>     and __lll_clocklock slight faster on fast-path (since it won't
>     require a function call anymore).

OK.

>   - Add lll_timedwait, which uses __lll_clocklock_wait, to replace both
>     __pause_nocancel and __nanosleep_nocancel.

OK.

> It also allows remove the sparc32 __lll_clocklock_wait implementation
> (since it is similar to the generic one).
> 
> Checked on x86_64-linux-gnu, sparcv9-linux-gnu, and i686-linux-gnu.
> ---
>  nptl/lll_timedlock_wait.c                    | 35 ++++++++--------
>  nptl/pthread_mutex_lock.c                    |  3 +-
>  nptl/pthread_mutex_timedlock.c               | 20 ++--------
>  sysdeps/nptl/lowlevellock.h                  | 15 ++++++-
>  sysdeps/sparc/sparc32/lll_timedlock_wait.c   |  1 -
>  sysdeps/sparc/sparc32/lowlevellock.c         | 42 --------------------
>  sysdeps/unix/sysv/linux/sparc/lowlevellock.h | 22 +++++++++-
>  7 files changed, 56 insertions(+), 82 deletions(-)
>  delete mode 100644 sysdeps/sparc/sparc32/lll_timedlock_wait.c
> 
> diff --git a/nptl/lll_timedlock_wait.c b/nptl/lll_timedlock_wait.c
> index cd3cc3d371..952b042555 100644
> --- a/nptl/lll_timedlock_wait.c
> +++ b/nptl/lll_timedlock_wait.c
> @@ -25,39 +25,38 @@
>  
>  
>  int
> -__lll_clocklock_wait (int *futex, clockid_t clockid,
> +__lll_clocklock_wait (int *futex, int val, clockid_t clockid,
>  		      const struct timespec *abstime, int private)
>  {
> -  /* Reject invalid timeouts.  */
> -  if (! valid_nanoseconds (abstime->tv_nsec))
> -    return EINVAL;
> +  struct timespec ts, *tsp = NULL;
>  
> -  /* Try locking.  */
> -  while (atomic_exchange_acq (futex, 2) != 0)
> +  if (abstime != NULL)
>      {
> -      struct timespec ts;
> +      /* Reject invalid timeouts.  */
> +      if (! valid_nanoseconds (abstime->tv_nsec))
> +        return EINVAL;
>  
> -      /* Get the current time. This can only fail if clockid is not
> -         valid.  */
> +      /* Get the current time. This can only fail if clockid is not valid.  */
>        if (__glibc_unlikely (__clock_gettime (clockid, &ts) != 0))
>          return EINVAL;
>  
>        /* Compute relative timeout.  */
> -      struct timespec rt;
> -      rt.tv_sec = abstime->tv_sec - ts.tv_sec;
> -      rt.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
> -      if (rt.tv_nsec < 0)
> +      ts.tv_sec = abstime->tv_sec - ts.tv_sec;
> +      ts.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
> +      if (ts.tv_nsec < 0)
>          {
> -          rt.tv_nsec += 1000000000;
> -          --rt.tv_sec;
> +	  ts.tv_nsec += 1000000000;
> +	  --ts.tv_sec;
>          }
>  
> -      if (rt.tv_sec < 0)
> +      if (ts.tv_sec < 0)
>          return ETIMEDOUT;
>  
> -      /* If *futex == 2, wait until woken or timeout.  */
> -      lll_futex_timed_wait (futex, 2, &rt, private);
> +      tsp = &ts;
>      }
>  
> +  /* If *futex == val, wait until woken or timeout.  */
> +  lll_futex_timed_wait (futex, val, tsp, private);
> +
>    return 0;
>  }

OK.

> diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
> index 0ab890d815..ace436d5a6 100644
> --- a/nptl/pthread_mutex_lock.c
> +++ b/nptl/pthread_mutex_lock.c
> @@ -434,7 +434,8 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
>  
>  		/* Delay the thread indefinitely.  */
>  		while (1)
> -		  __pause_nocancel ();
> +		  lll_timedwait (&(int){0}, 0, 0 /* ignored */, NULL,
> +				 private);

OK.

>  	      }
>  
>  	    oldval = mutex->__data.__lock;
> diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
> index c9bb3b9176..490064d8cf 100644
> --- a/nptl/pthread_mutex_timedlock.c
> +++ b/nptl/pthread_mutex_timedlock.c
> @@ -401,22 +401,10 @@ __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
>  
>  		    /* Delay the thread until the timeout is reached.
>  		       Then return ETIMEDOUT.  */
> -		    struct timespec reltime;
> -		    struct timespec now;
> -
> -		    INTERNAL_SYSCALL (clock_gettime, __err, 2, clockid,
> -				      &now);
> -		    reltime.tv_sec = abstime->tv_sec - now.tv_sec;
> -		    reltime.tv_nsec = abstime->tv_nsec - now.tv_nsec;
> -		    if (reltime.tv_nsec < 0)
> -		      {
> -			reltime.tv_nsec += 1000000000;
> -			--reltime.tv_sec;
> -		      }
> -		    if (reltime.tv_sec >= 0)
> -		      while (__nanosleep_nocancel (&reltime, &reltime) != 0)
> -			continue;
> -
> +		    do
> +		      e = lll_timedwait (&(int){0}, 0, clockid, abstime,
> +					 private);
> +		    while (e != ETIMEDOUT);

OK.

>  		    return ETIMEDOUT;
>  		  }
>  
> diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h
> index e3f006537a..92298f3b7e 100644
> --- a/sysdeps/nptl/lowlevellock.h
> +++ b/sysdeps/nptl/lowlevellock.h
> @@ -21,6 +21,7 @@
>  
>  #include <atomic.h>
>  #include <lowlevellock-futex.h>
> +#include <time.h>
>  
>  /* Low-level locks use a combination of atomic operations (to acquire and
>     release lock ownership) and futex operations (to block until the state
> @@ -121,10 +122,12 @@ extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
>  #define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
>  
>  
> -extern int __lll_clocklock_wait (int *futex, clockid_t,
> +extern int __lll_clocklock_wait (int *futex, int val, clockid_t,
>  				 const struct timespec *,
>  				 int private) attribute_hidden;
>  
> +#define lll_timedwait(futex, val, clockid, abstime, private)		\
> +  __lll_clocklock_wait (futex, val, clockid, abstime, private)

OK.

>  
>  /* As __lll_lock, but with an absolute timeout measured against the clock
>     specified in CLOCKID.  If the timeout occurs then return ETIMEDOUT. If
> @@ -136,7 +139,15 @@ extern int __lll_clocklock_wait (int *futex, clockid_t,
>                                                                  \
>      if (__glibc_unlikely                                        \
>          (atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
> -      __val = __lll_clocklock_wait (__futex, clockid, abstime, private); \
> +      {								\
> +	while (atomic_exchange_acq (futex, 2) != 0)		\
> +	  {							\
> +	    __val = __lll_clocklock_wait (__futex, 2, clockid, 	\
> +					  abstime, private);	\

OK.

> +	    if (__val == EINVAL || __val == ETIMEDOUT)		\
> +	      break;						\
> +	  }							\
> +      }								\
>      __val;                                                      \
>    })
>  #define lll_clocklock(futex, clockid, abstime, private)         \
> diff --git a/sysdeps/sparc/sparc32/lll_timedlock_wait.c b/sysdeps/sparc/sparc32/lll_timedlock_wait.c
> deleted file mode 100644
> index bd639a7091..0000000000
> --- a/sysdeps/sparc/sparc32/lll_timedlock_wait.c
> +++ /dev/null
> @@ -1 +0,0 @@
> -/* __lll_clocklock_wait is in lowlevellock.c.  */
> diff --git a/sysdeps/sparc/sparc32/lowlevellock.c b/sysdeps/sparc/sparc32/lowlevellock.c
> index 074ecf0636..1a0ab4d9f2 100644
> --- a/sysdeps/sparc/sparc32/lowlevellock.c
> +++ b/sysdeps/sparc/sparc32/lowlevellock.c
> @@ -50,46 +50,4 @@ __lll_lock_wait (int *futex, int private)
>      }
>    while (atomic_compare_and_exchange_val_24_acq (futex, 2, 0) != 0);
>  }
> -
> -
> -int
> -__lll_clocklock_wait (int *futex, clockid_t clockid,
> -                      const struct timespec *abstime, int private)
> -{
> -  /* Reject invalid timeouts.  */
> -  if (! valid_nanoseconds (abstime->tv_nsec))
> -    return EINVAL;
> -
> -  do
> -    {
> -      struct timespec ts;
> -      struct timespec rt;
> -
> -      /* Get the current time. This can only fail if clockid is not
> -         valid. */
> -      if (__glibc_unlikely (__clock_gettime (clockid, &ts) != 0))
> -        return EINVAL;
> -
> -      /* Compute relative timeout.  */
> -      rt.tv_sec = abstime->tv_sec - ts.tv_sec;
> -      rt.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
> -      if (rt.tv_nsec < 0)
> -	{
> -	  rt.tv_nsec += 1000000000;
> -	  --rt.tv_sec;
> -	}
> -
> -      /* Already timed out?  */
> -      if (rt.tv_sec < 0)
> -	return ETIMEDOUT;
> -
> -      /* Wait.  */
> -      int oldval = atomic_compare_and_exchange_val_24_acq (futex, 2, 1);
> -      if (oldval != 0)
> -	lll_futex_timed_wait (futex, 2, &rt, private);
> -    }
> -  while (atomic_compare_and_exchange_val_24_acq (futex, 2, 0) != 0);
> -
> -  return 0;
> -}

OK. Nice to see this code go.

>  #endif
> diff --git a/sysdeps/unix/sysv/linux/sparc/lowlevellock.h b/sysdeps/unix/sysv/linux/sparc/lowlevellock.h
> index 34441f8ff5..6c005e8ffa 100644
> --- a/sysdeps/unix/sysv/linux/sparc/lowlevellock.h
> +++ b/sysdeps/unix/sysv/linux/sparc/lowlevellock.h
> @@ -24,6 +24,7 @@
>  #include <bits/pthreadtypes.h>
>  #include <atomic.h>
>  #include <kernel-features.h>
> +#include <errno.h>
>  
>  #include <lowlevellock-futex.h>
>  
> @@ -75,9 +76,13 @@ __lll_cond_lock (int *futex, int private)
>  #define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
>  
>  
> -extern int __lll_clocklock_wait (int *futex, clockid_t, const struct timespec *,
> +extern int __lll_clocklock_wait (int *futex, clockid_t, int val,
> +				 const struct timespec *,
>  				 int private) attribute_hidden;
>  
> +#define lll_timedwait(futex, val, clockid, abstime, private)		\
> +  __lll_clocklock_wait (futex, val, clockid, abstime, private)
> +
>  static inline int
>  __attribute__ ((always_inline))
>  __lll_clocklock (int *futex, clockid_t clockid,
> @@ -87,7 +92,20 @@ __lll_clocklock (int *futex, clockid_t clockid,
>    int result = 0;
>  
>    if (__glibc_unlikely (val != 0))
> -    result = __lll_clocklock_wait (futex, clockid, abstime, private);
> +    {
> +      do
> +	{
> +	  int oldval = atomic_compare_and_exchange_val_24_acq (futex, val, 1);
> +	  if (oldval != 0)
> +	    {
> +	      result = __lll_clocklock_wait (futex, 2, clockid, abstime,
> +					     private);
> +	      if (result == EINVAL || result == ETIMEDOUT)
> +		break;
> +	    }
> +        }
> +      while (atomic_compare_and_exchange_val_24_acq (futex, val, 0) != 0);
> +    }
>    return result;
>  }
>  #define lll_clocklock(futex, clockid, abstime, private)  \
> 

OK.

Patch
diff mbox series

diff --git a/nptl/lll_timedlock_wait.c b/nptl/lll_timedlock_wait.c
index cd3cc3d371..952b042555 100644
--- a/nptl/lll_timedlock_wait.c
+++ b/nptl/lll_timedlock_wait.c
@@ -25,39 +25,38 @@ 
 
 
 int
-__lll_clocklock_wait (int *futex, clockid_t clockid,
+__lll_clocklock_wait (int *futex, int val, clockid_t clockid,
 		      const struct timespec *abstime, int private)
 {
-  /* Reject invalid timeouts.  */
-  if (! valid_nanoseconds (abstime->tv_nsec))
-    return EINVAL;
+  struct timespec ts, *tsp = NULL;
 
-  /* Try locking.  */
-  while (atomic_exchange_acq (futex, 2) != 0)
+  if (abstime != NULL)
     {
-      struct timespec ts;
+      /* Reject invalid timeouts.  */
+      if (! valid_nanoseconds (abstime->tv_nsec))
+        return EINVAL;
 
-      /* Get the current time. This can only fail if clockid is not
-         valid.  */
+      /* Get the current time. This can only fail if clockid is not valid.  */
       if (__glibc_unlikely (__clock_gettime (clockid, &ts) != 0))
         return EINVAL;
 
       /* Compute relative timeout.  */
-      struct timespec rt;
-      rt.tv_sec = abstime->tv_sec - ts.tv_sec;
-      rt.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
-      if (rt.tv_nsec < 0)
+      ts.tv_sec = abstime->tv_sec - ts.tv_sec;
+      ts.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
+      if (ts.tv_nsec < 0)
         {
-          rt.tv_nsec += 1000000000;
-          --rt.tv_sec;
+	  ts.tv_nsec += 1000000000;
+	  --ts.tv_sec;
         }
 
-      if (rt.tv_sec < 0)
+      if (ts.tv_sec < 0)
         return ETIMEDOUT;
 
-      /* If *futex == 2, wait until woken or timeout.  */
-      lll_futex_timed_wait (futex, 2, &rt, private);
+      tsp = &ts;
     }
 
+  /* If *futex == val, wait until woken or timeout.  */
+  lll_futex_timed_wait (futex, val, tsp, private);
+
   return 0;
 }
diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index 0ab890d815..ace436d5a6 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -434,7 +434,8 @@  __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 
 		/* Delay the thread indefinitely.  */
 		while (1)
-		  __pause_nocancel ();
+		  lll_timedwait (&(int){0}, 0, 0 /* ignored */, NULL,
+				 private);
 	      }
 
 	    oldval = mutex->__data.__lock;
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index c9bb3b9176..490064d8cf 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -401,22 +401,10 @@  __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
 
 		    /* Delay the thread until the timeout is reached.
 		       Then return ETIMEDOUT.  */
-		    struct timespec reltime;
-		    struct timespec now;
-
-		    INTERNAL_SYSCALL (clock_gettime, __err, 2, clockid,
-				      &now);
-		    reltime.tv_sec = abstime->tv_sec - now.tv_sec;
-		    reltime.tv_nsec = abstime->tv_nsec - now.tv_nsec;
-		    if (reltime.tv_nsec < 0)
-		      {
-			reltime.tv_nsec += 1000000000;
-			--reltime.tv_sec;
-		      }
-		    if (reltime.tv_sec >= 0)
-		      while (__nanosleep_nocancel (&reltime, &reltime) != 0)
-			continue;
-
+		    do
+		      e = lll_timedwait (&(int){0}, 0, clockid, abstime,
+					 private);
+		    while (e != ETIMEDOUT);
 		    return ETIMEDOUT;
 		  }
 
diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h
index e3f006537a..92298f3b7e 100644
--- a/sysdeps/nptl/lowlevellock.h
+++ b/sysdeps/nptl/lowlevellock.h
@@ -21,6 +21,7 @@ 
 
 #include <atomic.h>
 #include <lowlevellock-futex.h>
+#include <time.h>
 
 /* Low-level locks use a combination of atomic operations (to acquire and
    release lock ownership) and futex operations (to block until the state
@@ -121,10 +122,12 @@  extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
 #define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
 
 
-extern int __lll_clocklock_wait (int *futex, clockid_t,
+extern int __lll_clocklock_wait (int *futex, int val, clockid_t,
 				 const struct timespec *,
 				 int private) attribute_hidden;
 
+#define lll_timedwait(futex, val, clockid, abstime, private)		\
+  __lll_clocklock_wait (futex, val, clockid, abstime, private)
 
 /* As __lll_lock, but with an absolute timeout measured against the clock
    specified in CLOCKID.  If the timeout occurs then return ETIMEDOUT. If
@@ -136,7 +139,15 @@  extern int __lll_clocklock_wait (int *futex, clockid_t,
                                                                 \
     if (__glibc_unlikely                                        \
         (atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
-      __val = __lll_clocklock_wait (__futex, clockid, abstime, private); \
+      {								\
+	while (atomic_exchange_acq (futex, 2) != 0)		\
+	  {							\
+	    __val = __lll_clocklock_wait (__futex, 2, clockid, 	\
+					  abstime, private);	\
+	    if (__val == EINVAL || __val == ETIMEDOUT)		\
+	      break;						\
+	  }							\
+      }								\
     __val;                                                      \
   })
 #define lll_clocklock(futex, clockid, abstime, private)         \
diff --git a/sysdeps/sparc/sparc32/lll_timedlock_wait.c b/sysdeps/sparc/sparc32/lll_timedlock_wait.c
deleted file mode 100644
index bd639a7091..0000000000
--- a/sysdeps/sparc/sparc32/lll_timedlock_wait.c
+++ /dev/null
@@ -1 +0,0 @@ 
-/* __lll_clocklock_wait is in lowlevellock.c.  */
diff --git a/sysdeps/sparc/sparc32/lowlevellock.c b/sysdeps/sparc/sparc32/lowlevellock.c
index 074ecf0636..1a0ab4d9f2 100644
--- a/sysdeps/sparc/sparc32/lowlevellock.c
+++ b/sysdeps/sparc/sparc32/lowlevellock.c
@@ -50,46 +50,4 @@  __lll_lock_wait (int *futex, int private)
     }
   while (atomic_compare_and_exchange_val_24_acq (futex, 2, 0) != 0);
 }
-
-
-int
-__lll_clocklock_wait (int *futex, clockid_t clockid,
-                      const struct timespec *abstime, int private)
-{
-  /* Reject invalid timeouts.  */
-  if (! valid_nanoseconds (abstime->tv_nsec))
-    return EINVAL;
-
-  do
-    {
-      struct timespec ts;
-      struct timespec rt;
-
-      /* Get the current time. This can only fail if clockid is not
-         valid. */
-      if (__glibc_unlikely (__clock_gettime (clockid, &ts) != 0))
-        return EINVAL;
-
-      /* Compute relative timeout.  */
-      rt.tv_sec = abstime->tv_sec - ts.tv_sec;
-      rt.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
-      if (rt.tv_nsec < 0)
-	{
-	  rt.tv_nsec += 1000000000;
-	  --rt.tv_sec;
-	}
-
-      /* Already timed out?  */
-      if (rt.tv_sec < 0)
-	return ETIMEDOUT;
-
-      /* Wait.  */
-      int oldval = atomic_compare_and_exchange_val_24_acq (futex, 2, 1);
-      if (oldval != 0)
-	lll_futex_timed_wait (futex, 2, &rt, private);
-    }
-  while (atomic_compare_and_exchange_val_24_acq (futex, 2, 0) != 0);
-
-  return 0;
-}
 #endif
diff --git a/sysdeps/unix/sysv/linux/sparc/lowlevellock.h b/sysdeps/unix/sysv/linux/sparc/lowlevellock.h
index 34441f8ff5..6c005e8ffa 100644
--- a/sysdeps/unix/sysv/linux/sparc/lowlevellock.h
+++ b/sysdeps/unix/sysv/linux/sparc/lowlevellock.h
@@ -24,6 +24,7 @@ 
 #include <bits/pthreadtypes.h>
 #include <atomic.h>
 #include <kernel-features.h>
+#include <errno.h>
 
 #include <lowlevellock-futex.h>
 
@@ -75,9 +76,13 @@  __lll_cond_lock (int *futex, int private)
 #define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
 
 
-extern int __lll_clocklock_wait (int *futex, clockid_t, const struct timespec *,
+extern int __lll_clocklock_wait (int *futex, clockid_t, int val,
+				 const struct timespec *,
 				 int private) attribute_hidden;
 
+#define lll_timedwait(futex, val, clockid, abstime, private)		\
+  __lll_clocklock_wait (futex, val, clockid, abstime, private)
+
 static inline int
 __attribute__ ((always_inline))
 __lll_clocklock (int *futex, clockid_t clockid,
@@ -87,7 +92,20 @@  __lll_clocklock (int *futex, clockid_t clockid,
   int result = 0;
 
   if (__glibc_unlikely (val != 0))
-    result = __lll_clocklock_wait (futex, clockid, abstime, private);
+    {
+      do
+	{
+	  int oldval = atomic_compare_and_exchange_val_24_acq (futex, val, 1);
+	  if (oldval != 0)
+	    {
+	      result = __lll_clocklock_wait (futex, 2, clockid, abstime,
+					     private);
+	      if (result == EINVAL || result == ETIMEDOUT)
+		break;
+	    }
+        }
+      while (atomic_compare_and_exchange_val_24_acq (futex, val, 0) != 0);
+    }
   return result;
 }
 #define lll_clocklock(futex, clockid, abstime, private)  \