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

Message ID 20191030200052.497-3-adhemerval.zanella@linaro.org
State Accepted
Commit 215078017fd25fd64074e25ccd3dde0f6f19d4fe
Headers show
Series
  • [1/5] Consolidate futex-internal.h
Related show

Commit Message

Adhemerval Zanella Oct. 30, 2019, 8 p.m.
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

-- 
2.17.1

Comments

Carlos O'Donell Oct. 30, 2019, 9:08 p.m. | #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.

-- 
Cheers,
Carlos.

Patch

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)  \