Patchwork [1/7] nptl: Add clockid parameter to futex timed wait calls

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Submitter Mike Crowe
Date Feb. 27, 2019, 6:23 p.m.
Message ID <93715d4ac59e160bf7ef244832d56b062b78e425.1551291557.git-series.mac@mcrowe.com>
Download mbox | patch
Permalink /patch/31628/
State New
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Comments

Mike Crowe - Feb. 27, 2019, 6:23 p.m.
In preparation for adding POSIX clockwait variants of timedwait functions,
add a clockid_t parameter to futex_abstimed_wait functions and pass
CLOCK_REALTIME from all callers for the time being.

Replace lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset which
takes a clockid_t parameter rather than the magic clockbit.

* sysdeps/nptl/lowlevellock-futex.h,
  sysdeps/unix/sysv/linux/lowlevellock-futex.h: Replace
  lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset that takes a
  clockid rather than a special clockbit.

* sysdeps/nptl/lowlevellock-futex.h: Add lll_futex_supported_clockid so
  that client functions can check whether their clockid parameter is valid
  even if they don't ultimately end up calling lll_futex_clock_wait_bitset.

* sysdeps/nptl/futex-internal.h, sysdeps/unix/sysv/linux/futex-internal.h
  (futex_abstimed_wait, futex_abstimed_wait_cancelable): Add clockid_t
  parameter to indicate which clock the absolute time passed should be
  measured against. Pass that clockid onto lll_futex_clock_wait_bitset.
  Add invalid clock as reason for returning -EINVAL.

* sysdeps/nptl/futex-internal.h, sysdeps/unix/sysv/linux/futex-internal.h:
  Introduce futex_abstimed_supported_clockid so that client functions can
  check whether their clockid parameter is valid even if they don't
  ultimately end up calling futex_abstimed_wait.

* nptl/pthread_cond_wait.c (__pthread_cond_wait_common),
  nptl/pthread_rwlock_common (__pthread_rwlock_rdlock_full,
  __pthread_wrlock_full), nptl/sem_waitcommon (do_futex_wait): Pass
  additional CLOCK_REALTIME to futex_abstimed_wait_cancelable.

* nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Switch to
  lll_futex_clock_wait_bitset and pass CLOCK_REALTIME
---
 nptl/pthread_cond_wait.c                     |  2 +-
 nptl/pthread_mutex_timedlock.c               |  8 +++---
 nptl/pthread_rwlock_common.c                 |  8 +++---
 nptl/sem_waitcommon.c                        |  6 ++--
 sysdeps/nptl/futex-internal.h                |  7 +++++-
 sysdeps/nptl/lowlevellock-futex.h            | 14 ++++++----
 sysdeps/unix/sysv/linux/futex-internal.h     | 26 +++++++++++++------
 sysdeps/unix/sysv/linux/lowlevellock-futex.h | 29 ++++++++++++++++-----
 8 files changed, 71 insertions(+), 29 deletions(-)
Adhemerval Zanella Netto - March 5, 2019, 12:39 p.m.
On 27/02/2019 15:23, Mike Crowe wrote:
> In preparation for adding POSIX clockwait variants of timedwait functions,
> add a clockid_t parameter to futex_abstimed_wait functions and pass
> CLOCK_REALTIME from all callers for the time being.
> 
> Replace lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset which
> takes a clockid_t parameter rather than the magic clockbit.
> 
> * sysdeps/nptl/lowlevellock-futex.h,
>   sysdeps/unix/sysv/linux/lowlevellock-futex.h: Replace
>   lll_futex_timed_wait_bitset with lll_futex_clock_wait_bitset that takes a
>   clockid rather than a special clockbit.
> 
> * sysdeps/nptl/lowlevellock-futex.h: Add lll_futex_supported_clockid so
>   that client functions can check whether their clockid parameter is valid
>   even if they don't ultimately end up calling lll_futex_clock_wait_bitset.
> 
> * sysdeps/nptl/futex-internal.h, sysdeps/unix/sysv/linux/futex-internal.h
>   (futex_abstimed_wait, futex_abstimed_wait_cancelable): Add clockid_t
>   parameter to indicate which clock the absolute time passed should be
>   measured against. Pass that clockid onto lll_futex_clock_wait_bitset.
>   Add invalid clock as reason for returning -EINVAL.
> 
> * sysdeps/nptl/futex-internal.h, sysdeps/unix/sysv/linux/futex-internal.h:
>   Introduce futex_abstimed_supported_clockid so that client functions can
>   check whether their clockid parameter is valid even if they don't
>   ultimately end up calling futex_abstimed_wait.
> 
> * nptl/pthread_cond_wait.c (__pthread_cond_wait_common),
>   nptl/pthread_rwlock_common (__pthread_rwlock_rdlock_full,
>   __pthread_wrlock_full), nptl/sem_waitcommon (do_futex_wait): Pass
>   additional CLOCK_REALTIME to futex_abstimed_wait_cancelable.
> 
> * nptl/pthread_mutex_timedlock.c (__pthread_mutex_timedlock): Switch to
>   lll_futex_clock_wait_bitset and pass CLOCK_REALTIME
> ---
>  nptl/pthread_cond_wait.c                     |  2 +-
>  nptl/pthread_mutex_timedlock.c               |  8 +++---
>  nptl/pthread_rwlock_common.c                 |  8 +++---
>  nptl/sem_waitcommon.c                        |  6 ++--
>  sysdeps/nptl/futex-internal.h                |  7 +++++-
>  sysdeps/nptl/lowlevellock-futex.h            | 14 ++++++----
>  sysdeps/unix/sysv/linux/futex-internal.h     | 26 +++++++++++++------
>  sysdeps/unix/sysv/linux/lowlevellock-futex.h | 29 ++++++++++++++++-----
>  8 files changed, 71 insertions(+), 29 deletions(-)
> 
> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
> index 9a0f29e..daa4e25 100644
> --- a/nptl/pthread_cond_wait.c
> +++ b/nptl/pthread_cond_wait.c
> @@ -537,7 +537,7 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
>  		{
>  		  /* Use CLOCK_REALTIME.  */
>  		  err = futex_abstimed_wait_cancelable
> -		      (cond->__data.__g_signals + g, 0, abstime, private);
> +		      (cond->__data.__g_signals + g, 0, CLOCK_REALTIME, abstime, private);
>  		}
>  	    }
>  

Since we still assume that an architecture might not support futex
with CLOCK_REALTIME, this part should check for __ASSUME_FUTEX_CLOCK_REALTIME
as other parts.

I proposed recently to just assume __ASSUME_FUTEX_CLOCK_REALTIME
support [1], which simplifies this patch.

[1] https://sourceware.org/ml/libc-alpha/2019-02/msg00667.html

> diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
> index 2f61a7d..c145a65 100644
> --- a/nptl/pthread_mutex_timedlock.c
> +++ b/nptl/pthread_mutex_timedlock.c
> @@ -241,7 +241,7 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
>  	  if (__glibc_unlikely (abstime->tv_sec < 0))
>  	    return ETIMEDOUT;
>  #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
> -     || !defined lll_futex_timed_wait_bitset)
> +     || !defined lll_futex_clock_wait_bitset)
>  	  struct timeval tv;
>  	  struct timespec rt;
>  
> @@ -288,12 +288,12 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
>  
>  	  /* Block using the futex.  */
>  #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
> -     || !defined lll_futex_timed_wait_bitset)
> +     || !defined lll_futex_clock_wait_bitset)
>  	  lll_futex_timed_wait (&mutex->__data.__lock, oldval,
>  				&rt, PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
>  #else
> -	  int err = lll_futex_timed_wait_bitset (&mutex->__data.__lock,
> -	      oldval, abstime, FUTEX_CLOCK_REALTIME,
> +	  int err = lll_futex_clock_wait_bitset (&mutex->__data.__lock,
> +	      oldval, CLOCK_REALTIME, abstime,
>  	      PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
>  	  /* The futex call timed out.  */
>  	  if (err == -ETIMEDOUT)
> diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
> index 2560734..89ba21a 100644
> --- a/nptl/pthread_rwlock_common.c
> +++ b/nptl/pthread_rwlock_common.c
> @@ -319,7 +319,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
>  		{
>  		  int private = __pthread_rwlock_get_private (rwlock);
>  		  int err = futex_abstimed_wait (&rwlock->__data.__readers,
> -						 r, abstime, private);
> +						 r, CLOCK_REALTIME, abstime, private);
>  		  /* We ignore EAGAIN and EINTR.  On time-outs, we can just
>  		     return because we don't need to clean up anything.  */
>  		  if (err == ETIMEDOUT)
> @@ -447,7 +447,7 @@ __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
>  	    continue;
>  	  int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
>  					 1 | PTHREAD_RWLOCK_FUTEX_USED,
> -					 abstime, private);
> +					 CLOCK_REALTIME, abstime, private);
>  	  if (err == ETIMEDOUT)
>  	    {
>  	      /* If we timed out, we need to unregister.  If no read phase
> @@ -707,7 +707,7 @@ __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
>  	  may_share_futex_used_flag = true;
>  	  int err = futex_abstimed_wait (&rwlock->__data.__writers_futex,
>  					 1 | PTHREAD_RWLOCK_FUTEX_USED,
> -					 abstime, private);
> +					 CLOCK_REALTIME, abstime, private);
>  	  if (err == ETIMEDOUT)
>  	    {
>  	      if (prefer_writer)
> @@ -806,7 +806,7 @@ __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
>  	    continue;
>  	  int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
>  					 PTHREAD_RWLOCK_FUTEX_USED,
> -					 abstime, private);
> +					 CLOCK_REALTIME, abstime, private);
>  	  if (err == ETIMEDOUT)
>  	    {
>  	      if (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP)
> diff --git a/nptl/sem_waitcommon.c b/nptl/sem_waitcommon.c
> index 5646bea..425d040 100644
> --- a/nptl/sem_waitcommon.c
> +++ b/nptl/sem_waitcommon.c
> @@ -109,11 +109,13 @@ do_futex_wait (struct new_sem *sem, const struct timespec *abstime)
>  
>  #if __HAVE_64B_ATOMICS
>    err = futex_abstimed_wait_cancelable (
> -      (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0, abstime,
> +      (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0,
> +      CLOCK_REALTIME, abstime,
>        sem->private);
>  #else
>    err = futex_abstimed_wait_cancelable (&sem->value, SEM_NWAITERS_MASK,
> -					abstime, sem->private);
> +					CLOCK_REALTIME, abstime,
> +					sem->private);
>  #endif
>  
>    return err;
> diff --git a/sysdeps/nptl/futex-internal.h b/sysdeps/nptl/futex-internal.h
> index 86a0818..54b7319 100644
> --- a/sysdeps/nptl/futex-internal.h
> +++ b/sysdeps/nptl/futex-internal.h
> @@ -159,16 +159,23 @@ futex_reltimed_wait_cancelable (unsigned int* futex_word,
>  				unsigned int expected,
>  			        const struct timespec* reltime, int private);
>  
> +/* Check whether the specified clockid is supported by
> +   futex_abstimed_wait and futex_abstimed_wait_cancelable. */
> +static __always_inline int
> +futex_abstimed_supported_clockid (clockid_t clockid);
> +
>  /* Like futex_reltimed_wait, but the provided timeout (ABSTIME) is an
>     absolute point in time; a call will time out after this point in time.  */
>  static __always_inline int
>  futex_abstimed_wait (unsigned int* futex_word, unsigned int expected,
> +		     clockid_t clockid,
>  		     const struct timespec* abstime, int private);
>  
>  /* Like futex_reltimed_wait but is a POSIX cancellation point.  */
>  static __always_inline int
>  futex_abstimed_wait_cancelable (unsigned int* futex_word,
>  				unsigned int expected,
> +				clockid_t clockid,
>  			        const struct timespec* abstime, int private);
>  
>  /* Atomically wrt other futex operations on the same futex, this unblocks the
> diff --git a/sysdeps/nptl/lowlevellock-futex.h b/sysdeps/nptl/lowlevellock-futex.h
> index bb8effe..35fcfbb 100644
> --- a/sysdeps/nptl/lowlevellock-futex.h
> +++ b/sysdeps/nptl/lowlevellock-futex.h
> @@ -43,11 +43,15 @@
>  #define lll_futex_timed_wait(futexp, val, timeout, private)             \
>    -ENOSYS
>  
> -/* This macro should be defined only if FUTEX_CLOCK_REALTIME is also defined.
> -   If CLOCKBIT is zero, this is identical to lll_futex_timed_wait.
> -   If CLOCKBIT has FUTEX_CLOCK_REALTIME set, then it's the same but
> -   TIMEOUT is counted by CLOCK_REALTIME rather than CLOCK_MONOTONIC.  */
> -#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
> +/* Verify whether the supplied clockid is supported by
> +   lll_futex_clock_wait_bitset */
> +#define lll_futex_supported_clockid(clockid)				\
> +  (0)
> +
> +/* Wait until a lll_futex_wake call on FUTEXP, or the absolute TIMEOUT
> +   measured against CLOCKID elapses. CLOCKID may be CLOCK_REALTIME or
> +   CLOCK_MONOTONIC. */
> +#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
>    -ENOSYS
>  
>  /* Wake up up to NR waiters on FUTEXP.  */
> diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
> index 55f0fab..68bfe7e 100644
> --- a/sysdeps/unix/sysv/linux/futex-internal.h
> +++ b/sysdeps/unix/sysv/linux/futex-internal.h
> @@ -162,15 +162,24 @@ futex_reltimed_wait_cancelable (unsigned int *futex_word,
>  
>  /* See sysdeps/nptl/futex-internal.h for details.  */
>  static __always_inline int
> +futex_abstimed_supported_clockid (clockid_t clockid)
> +{
> +  return lll_futex_supported_clockid (clockid);
> +}
> +
> +/* See sysdeps/nptl/futex-internal.h for details.  */
> +static __always_inline int
>  futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
> +		     clockid_t clockid,
>  		     const struct timespec *abstime, int private)
>  {
>    /* Work around the fact that the kernel rejects negative timeout values
>       despite them being valid.  */
>    if (__glibc_unlikely ((abstime != NULL) && (abstime->tv_sec < 0)))
>      return ETIMEDOUT;
> -  int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
> -					 FUTEX_CLOCK_REALTIME, private);
> +  int err = lll_futex_clock_wait_bitset (futex_word, expected,
> +					 clockid, abstime,
> +					 private);
>    switch (err)
>      {
>      case 0:
> @@ -180,9 +189,10 @@ futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
>        return -err;
>  
>      case -EFAULT: /* Must have been caused by a glibc or application bug.  */
> -    case -EINVAL: /* Either due to wrong alignment or due to the timeout not
> -		     being normalized.  Must have been caused by a glibc or
> -		     application bug.  */
> +    case -EINVAL: /* Either due to wrong alignment, unsupported
> +		     clockid or due to the timeout not being
> +		     normalized. Must have been caused by a glibc or
> +		     application bug. */
>      case -ENOSYS: /* Must have been caused by a glibc bug.  */
>      /* No other errors are documented at this time.  */
>      default:
> @@ -194,6 +204,7 @@ futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
>  static __always_inline int
>  futex_abstimed_wait_cancelable (unsigned int *futex_word,
>  				unsigned int expected,
> +				clockid_t clockid,
>  			        const struct timespec *abstime, int private)
>  {
>    /* Work around the fact that the kernel rejects negative timeout values
> @@ -202,8 +213,9 @@ futex_abstimed_wait_cancelable (unsigned int *futex_word,
>      return ETIMEDOUT;
>    int oldtype;
>    oldtype = __pthread_enable_asynccancel ();
> -  int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
> -					 FUTEX_CLOCK_REALTIME, private);
> +  int err = lll_futex_clock_wait_bitset (futex_word, expected,
> +					clockid, abstime,
> +					private);
>    __pthread_disable_asynccancel (oldtype);
>    switch (err)
>      {
> diff --git a/sysdeps/unix/sysv/linux/lowlevellock-futex.h b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> index 6f060b1..c3e7152 100644
> --- a/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> +++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> @@ -82,12 +82,29 @@
>  		     __lll_private_flag (FUTEX_WAIT, private),  \
>  		     val, timeout)
>  
> -#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
> -  lll_futex_syscall (6, futexp,                                         \
> -		     __lll_private_flag (FUTEX_WAIT_BITSET | (clockbit), \
> -					 private),                      \
> -		     val, timeout, NULL /* Unused.  */,                 \
> -		     FUTEX_BITSET_MATCH_ANY)
> +/* Verify whether the supplied clockid is supported by
> +   lll_futex_clock_wait_bitset */
> +#define lll_futex_supported_clockid(clockid)			\
> +  (clockid == CLOCK_REALTIME || clockid == CLOCK_MONOTONIC)

I think we need evaluate clockid with parentesis to avoid some macro
evaluation issues.

> +
> +/* The kernel currently only supports CLOCK_MONOTONIC or
> + * CLOCK_REALTIME timeouts for FUTEX_WAIT_BITSET. We could attempt to
> + * convert others here but currently do not.
> + */
> +#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
> +  ({									\
> +    long int __ret;							\
> +    if (lll_futex_supported_clockid (clockid)) {			\

I think even for macro definitions we need to use GNU style for brackets
(which means break in a subsequent line).

> +      const unsigned int clockbit = (clockid == CLOCK_REALTIME) ? FUTEX_CLOCK_REALTIME : 0; \
> +      __ret = lll_futex_syscall (6, futexp,				\
> +				 __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, \
> +						     private),		\
> +				 val, timeout, NULL /* Unused.  */,	\
> +				 FUTEX_BITSET_MATCH_ANY);		\
> +    } else								\
> +      __ret = -EINVAL;							\
> +    __ret;								\
> +  })
>  
>  #define lll_futex_wake(futexp, nr, private)                             \
>    lll_futex_syscall (4, futexp,                                         \
>
Mike Crowe - March 10, 2019, 8:59 a.m.
On Tuesday 05 March 2019 at 09:39:58 -0300, Adhemerval Zanella wrote:
> > diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
> > index 9a0f29e..daa4e25 100644
> > --- a/nptl/pthread_cond_wait.c
> > +++ b/nptl/pthread_cond_wait.c
> > @@ -537,7 +537,7 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
> >  		{
> >  		  /* Use CLOCK_REALTIME.  */
> >  		  err = futex_abstimed_wait_cancelable
> > -		      (cond->__data.__g_signals + g, 0, abstime, private);
> > +		      (cond->__data.__g_signals + g, 0, CLOCK_REALTIME, abstime, private);
> >  		}
> >  	    }
> >  
> 
> Since we still assume that an architecture might not support futex
> with CLOCK_REALTIME, this part should check for __ASSUME_FUTEX_CLOCK_REALTIME
> as other parts.
> 
> I proposed recently to just assume __ASSUME_FUTEX_CLOCK_REALTIME
> support [1], which simplifies this patch.

Whilst trying to implement pthread_mutex_clockclock offline yesterday, I
decided to propose the same thing. It looks like I don't need to. :)

> [1] https://sourceware.org/ml/libc-alpha/2019-02/msg00667.html

It would certainly make my life easier if that patch was merged.

Thanks.

Mike.
Adhemerval Zanella Netto - March 11, 2019, 11:50 a.m.
On 10/03/2019 05:59, Mike Crowe wrote:
> On Tuesday 05 March 2019 at 09:39:58 -0300, Adhemerval Zanella wrote:
>>> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
>>> index 9a0f29e..daa4e25 100644
>>> --- a/nptl/pthread_cond_wait.c
>>> +++ b/nptl/pthread_cond_wait.c
>>> @@ -537,7 +537,7 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
>>>  		{
>>>  		  /* Use CLOCK_REALTIME.  */
>>>  		  err = futex_abstimed_wait_cancelable
>>> -		      (cond->__data.__g_signals + g, 0, abstime, private);
>>> +		      (cond->__data.__g_signals + g, 0, CLOCK_REALTIME, abstime, private);
>>>  		}
>>>  	    }
>>>  
>>
>> Since we still assume that an architecture might not support futex
>> with CLOCK_REALTIME, this part should check for __ASSUME_FUTEX_CLOCK_REALTIME
>> as other parts.
>>
>> I proposed recently to just assume __ASSUME_FUTEX_CLOCK_REALTIME
>> support [1], which simplifies this patch.
> 
> Whilst trying to implement pthread_mutex_clockclock offline yesterday, I
> decided to propose the same thing. It looks like I don't need to. :)
> 
>> [1] https://sourceware.org/ml/libc-alpha/2019-02/msg00667.html
> 
> It would certainly make my life easier if that patch was merged.
> 
> Thanks.

It is already merged.

Patch

diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
index 9a0f29e..daa4e25 100644
--- a/nptl/pthread_cond_wait.c
+++ b/nptl/pthread_cond_wait.c
@@ -537,7 +537,7 @@  __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
 		{
 		  /* Use CLOCK_REALTIME.  */
 		  err = futex_abstimed_wait_cancelable
-		      (cond->__data.__g_signals + g, 0, abstime, private);
+		      (cond->__data.__g_signals + g, 0, CLOCK_REALTIME, abstime, private);
 		}
 	    }
 
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index 2f61a7d..c145a65 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -241,7 +241,7 @@  __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 	  if (__glibc_unlikely (abstime->tv_sec < 0))
 	    return ETIMEDOUT;
 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
-     || !defined lll_futex_timed_wait_bitset)
+     || !defined lll_futex_clock_wait_bitset)
 	  struct timeval tv;
 	  struct timespec rt;
 
@@ -288,12 +288,12 @@  __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 
 	  /* Block using the futex.  */
 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
-     || !defined lll_futex_timed_wait_bitset)
+     || !defined lll_futex_clock_wait_bitset)
 	  lll_futex_timed_wait (&mutex->__data.__lock, oldval,
 				&rt, PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 #else
-	  int err = lll_futex_timed_wait_bitset (&mutex->__data.__lock,
-	      oldval, abstime, FUTEX_CLOCK_REALTIME,
+	  int err = lll_futex_clock_wait_bitset (&mutex->__data.__lock,
+	      oldval, CLOCK_REALTIME, abstime,
 	      PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
 	  /* The futex call timed out.  */
 	  if (err == -ETIMEDOUT)
diff --git a/nptl/pthread_rwlock_common.c b/nptl/pthread_rwlock_common.c
index 2560734..89ba21a 100644
--- a/nptl/pthread_rwlock_common.c
+++ b/nptl/pthread_rwlock_common.c
@@ -319,7 +319,7 @@  __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
 		{
 		  int private = __pthread_rwlock_get_private (rwlock);
 		  int err = futex_abstimed_wait (&rwlock->__data.__readers,
-						 r, abstime, private);
+						 r, CLOCK_REALTIME, abstime, private);
 		  /* We ignore EAGAIN and EINTR.  On time-outs, we can just
 		     return because we don't need to clean up anything.  */
 		  if (err == ETIMEDOUT)
@@ -447,7 +447,7 @@  __pthread_rwlock_rdlock_full (pthread_rwlock_t *rwlock,
 	    continue;
 	  int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
 					 1 | PTHREAD_RWLOCK_FUTEX_USED,
-					 abstime, private);
+					 CLOCK_REALTIME, abstime, private);
 	  if (err == ETIMEDOUT)
 	    {
 	      /* If we timed out, we need to unregister.  If no read phase
@@ -707,7 +707,7 @@  __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
 	  may_share_futex_used_flag = true;
 	  int err = futex_abstimed_wait (&rwlock->__data.__writers_futex,
 					 1 | PTHREAD_RWLOCK_FUTEX_USED,
-					 abstime, private);
+					 CLOCK_REALTIME, abstime, private);
 	  if (err == ETIMEDOUT)
 	    {
 	      if (prefer_writer)
@@ -806,7 +806,7 @@  __pthread_rwlock_wrlock_full (pthread_rwlock_t *rwlock,
 	    continue;
 	  int err = futex_abstimed_wait (&rwlock->__data.__wrphase_futex,
 					 PTHREAD_RWLOCK_FUTEX_USED,
-					 abstime, private);
+					 CLOCK_REALTIME, abstime, private);
 	  if (err == ETIMEDOUT)
 	    {
 	      if (rwlock->__data.__flags != PTHREAD_RWLOCK_PREFER_READER_NP)
diff --git a/nptl/sem_waitcommon.c b/nptl/sem_waitcommon.c
index 5646bea..425d040 100644
--- a/nptl/sem_waitcommon.c
+++ b/nptl/sem_waitcommon.c
@@ -109,11 +109,13 @@  do_futex_wait (struct new_sem *sem, const struct timespec *abstime)
 
 #if __HAVE_64B_ATOMICS
   err = futex_abstimed_wait_cancelable (
-      (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0, abstime,
+      (unsigned int *) &sem->data + SEM_VALUE_OFFSET, 0,
+      CLOCK_REALTIME, abstime,
       sem->private);
 #else
   err = futex_abstimed_wait_cancelable (&sem->value, SEM_NWAITERS_MASK,
-					abstime, sem->private);
+					CLOCK_REALTIME, abstime,
+					sem->private);
 #endif
 
   return err;
diff --git a/sysdeps/nptl/futex-internal.h b/sysdeps/nptl/futex-internal.h
index 86a0818..54b7319 100644
--- a/sysdeps/nptl/futex-internal.h
+++ b/sysdeps/nptl/futex-internal.h
@@ -159,16 +159,23 @@  futex_reltimed_wait_cancelable (unsigned int* futex_word,
 				unsigned int expected,
 			        const struct timespec* reltime, int private);
 
+/* Check whether the specified clockid is supported by
+   futex_abstimed_wait and futex_abstimed_wait_cancelable. */
+static __always_inline int
+futex_abstimed_supported_clockid (clockid_t clockid);
+
 /* Like futex_reltimed_wait, but the provided timeout (ABSTIME) is an
    absolute point in time; a call will time out after this point in time.  */
 static __always_inline int
 futex_abstimed_wait (unsigned int* futex_word, unsigned int expected,
+		     clockid_t clockid,
 		     const struct timespec* abstime, int private);
 
 /* Like futex_reltimed_wait but is a POSIX cancellation point.  */
 static __always_inline int
 futex_abstimed_wait_cancelable (unsigned int* futex_word,
 				unsigned int expected,
+				clockid_t clockid,
 			        const struct timespec* abstime, int private);
 
 /* Atomically wrt other futex operations on the same futex, this unblocks the
diff --git a/sysdeps/nptl/lowlevellock-futex.h b/sysdeps/nptl/lowlevellock-futex.h
index bb8effe..35fcfbb 100644
--- a/sysdeps/nptl/lowlevellock-futex.h
+++ b/sysdeps/nptl/lowlevellock-futex.h
@@ -43,11 +43,15 @@ 
 #define lll_futex_timed_wait(futexp, val, timeout, private)             \
   -ENOSYS
 
-/* This macro should be defined only if FUTEX_CLOCK_REALTIME is also defined.
-   If CLOCKBIT is zero, this is identical to lll_futex_timed_wait.
-   If CLOCKBIT has FUTEX_CLOCK_REALTIME set, then it's the same but
-   TIMEOUT is counted by CLOCK_REALTIME rather than CLOCK_MONOTONIC.  */
-#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
+/* Verify whether the supplied clockid is supported by
+   lll_futex_clock_wait_bitset */
+#define lll_futex_supported_clockid(clockid)				\
+  (0)
+
+/* Wait until a lll_futex_wake call on FUTEXP, or the absolute TIMEOUT
+   measured against CLOCKID elapses. CLOCKID may be CLOCK_REALTIME or
+   CLOCK_MONOTONIC. */
+#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
   -ENOSYS
 
 /* Wake up up to NR waiters on FUTEXP.  */
diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
index 55f0fab..68bfe7e 100644
--- a/sysdeps/unix/sysv/linux/futex-internal.h
+++ b/sysdeps/unix/sysv/linux/futex-internal.h
@@ -162,15 +162,24 @@  futex_reltimed_wait_cancelable (unsigned int *futex_word,
 
 /* See sysdeps/nptl/futex-internal.h for details.  */
 static __always_inline int
+futex_abstimed_supported_clockid (clockid_t clockid)
+{
+  return lll_futex_supported_clockid (clockid);
+}
+
+/* See sysdeps/nptl/futex-internal.h for details.  */
+static __always_inline int
 futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
+		     clockid_t clockid,
 		     const struct timespec *abstime, int private)
 {
   /* Work around the fact that the kernel rejects negative timeout values
      despite them being valid.  */
   if (__glibc_unlikely ((abstime != NULL) && (abstime->tv_sec < 0)))
     return ETIMEDOUT;
-  int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
-					 FUTEX_CLOCK_REALTIME, private);
+  int err = lll_futex_clock_wait_bitset (futex_word, expected,
+					 clockid, abstime,
+					 private);
   switch (err)
     {
     case 0:
@@ -180,9 +189,10 @@  futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
       return -err;
 
     case -EFAULT: /* Must have been caused by a glibc or application bug.  */
-    case -EINVAL: /* Either due to wrong alignment or due to the timeout not
-		     being normalized.  Must have been caused by a glibc or
-		     application bug.  */
+    case -EINVAL: /* Either due to wrong alignment, unsupported
+		     clockid or due to the timeout not being
+		     normalized. Must have been caused by a glibc or
+		     application bug. */
     case -ENOSYS: /* Must have been caused by a glibc bug.  */
     /* No other errors are documented at this time.  */
     default:
@@ -194,6 +204,7 @@  futex_abstimed_wait (unsigned int *futex_word, unsigned int expected,
 static __always_inline int
 futex_abstimed_wait_cancelable (unsigned int *futex_word,
 				unsigned int expected,
+				clockid_t clockid,
 			        const struct timespec *abstime, int private)
 {
   /* Work around the fact that the kernel rejects negative timeout values
@@ -202,8 +213,9 @@  futex_abstimed_wait_cancelable (unsigned int *futex_word,
     return ETIMEDOUT;
   int oldtype;
   oldtype = __pthread_enable_asynccancel ();
-  int err = lll_futex_timed_wait_bitset (futex_word, expected, abstime,
-					 FUTEX_CLOCK_REALTIME, private);
+  int err = lll_futex_clock_wait_bitset (futex_word, expected,
+					clockid, abstime,
+					private);
   __pthread_disable_asynccancel (oldtype);
   switch (err)
     {
diff --git a/sysdeps/unix/sysv/linux/lowlevellock-futex.h b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
index 6f060b1..c3e7152 100644
--- a/sysdeps/unix/sysv/linux/lowlevellock-futex.h
+++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
@@ -82,12 +82,29 @@ 
 		     __lll_private_flag (FUTEX_WAIT, private),  \
 		     val, timeout)
 
-#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
-  lll_futex_syscall (6, futexp,                                         \
-		     __lll_private_flag (FUTEX_WAIT_BITSET | (clockbit), \
-					 private),                      \
-		     val, timeout, NULL /* Unused.  */,                 \
-		     FUTEX_BITSET_MATCH_ANY)
+/* Verify whether the supplied clockid is supported by
+   lll_futex_clock_wait_bitset */
+#define lll_futex_supported_clockid(clockid)			\
+  (clockid == CLOCK_REALTIME || clockid == CLOCK_MONOTONIC)
+
+/* The kernel currently only supports CLOCK_MONOTONIC or
+ * CLOCK_REALTIME timeouts for FUTEX_WAIT_BITSET. We could attempt to
+ * convert others here but currently do not.
+ */
+#define lll_futex_clock_wait_bitset(futexp, val, clockid, timeout, private) \
+  ({									\
+    long int __ret;							\
+    if (lll_futex_supported_clockid (clockid)) {			\
+      const unsigned int clockbit = (clockid == CLOCK_REALTIME) ? FUTEX_CLOCK_REALTIME : 0; \
+      __ret = lll_futex_syscall (6, futexp,				\
+				 __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, \
+						     private),		\
+				 val, timeout, NULL /* Unused.  */,	\
+				 FUTEX_BITSET_MATCH_ANY);		\
+    } else								\
+      __ret = -EINVAL;							\
+    __ret;								\
+  })
 
 #define lll_futex_wake(futexp, nr, private)                             \
   lll_futex_syscall (4, futexp,                                         \