Patchwork [v3,1/6] nptl: Add clockid parameter to futex timed wait calls

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Submitter Mike Crowe
Date May 27, 2019, 8:03 p.m.
Message ID <95894abea465528f7bd5f8c0971c80f0ccdd73f7.1558987219.git-series.mac@mcrowe.com>
Download mbox | patch
Permalink /patch/32864/
State New
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Comments

Mike Crowe - May 27, 2019, 8:03 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): Remove code to
  calculate relative timeout for __PTHREAD_COND_CLOCK_MONOTONIC_MASK and
  just pass CLOCK_MONOTONIC or CLOCK_REALTIME as required to
  futex_abstimed_wait_cancelable.

* 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
---
 ChangeLog                                    | 40 +++++++++++++++++++++-
 nptl/pthread_cond_wait.c                     | 32 +++--------------
 nptl/pthread_mutex_timedlock.c               |  4 +-
 nptl/pthread_rwlock_common.c                 |  8 ++--
 nptl/sem_waitcommon.c                        |  6 ++-
 sysdeps/nptl/futex-internal.h                |  7 ++++-
 sysdeps/nptl/lowlevellock-futex.h            | 13 ++++---
 sysdeps/unix/sysv/linux/futex-internal.h     | 26 ++++++++++----
 sysdeps/unix/sysv/linux/lowlevellock-futex.h | 33 +++++++++++++----
 9 files changed, 118 insertions(+), 51 deletions(-)
Adhemerval Zanella Netto - June 5, 2019, 5:52 p.m.
On 27/05/2019 17:03, 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): Remove code to
>   calculate relative timeout for __PTHREAD_COND_CLOCK_MONOTONIC_MASK and
>   just pass CLOCK_MONOTONIC or CLOCK_REALTIME as required to
>   futex_abstimed_wait_cancelable.
> 
> * 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
> ---
>  ChangeLog                                    | 40 +++++++++++++++++++++-
>  nptl/pthread_cond_wait.c                     | 32 +++--------------
>  nptl/pthread_mutex_timedlock.c               |  4 +-
>  nptl/pthread_rwlock_common.c                 |  8 ++--
>  nptl/sem_waitcommon.c                        |  6 ++-
>  sysdeps/nptl/futex-internal.h                |  7 ++++-
>  sysdeps/nptl/lowlevellock-futex.h            | 13 ++++---
>  sysdeps/unix/sysv/linux/futex-internal.h     | 26 ++++++++++----
>  sysdeps/unix/sysv/linux/lowlevellock-futex.h | 33 +++++++++++++----
>  9 files changed, 118 insertions(+), 51 deletions(-)
> 
> diff --git a/ChangeLog b/ChangeLog
> index 53a3ae4..ff85b12 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,3 +1,43 @@
> +2019-05-27  Mike Crowe  <mac@mcrowe.com>
> +
> +	nptl: Add clockid parameter to futex timed wait calls
> +
> +	* 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): Remove
> +	code to calculate relative timeout for
> +	__PTHREAD_COND_CLOCK_MONOTONIC_MASK and just pass CLOCK_MONOTONIC
> +	or CLOCK_REALTIME as required to futex_abstimed_wait_cancelable.
> +
> +	* 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
> +
>  2019-05-27  Florian Weimer  <fweimer@redhat.com>
>  
>  	* nptl/nptl-init.c: Add comment.
> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
> index 9a0f29e..7385562 100644
> --- a/nptl/pthread_cond_wait.c
> +++ b/nptl/pthread_cond_wait.c
> @@ -509,35 +509,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
>  		 values despite them being valid.  */
>  	      if (__glibc_unlikely (abstime->tv_sec < 0))
>  	        err = ETIMEDOUT;
> -
> -	      else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
> -		{
> -		  /* CLOCK_MONOTONIC is requested.  */
> -		  struct timespec rt;
> -		  if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
> -		    __libc_fatal ("clock_gettime does not support "
> -				  "CLOCK_MONOTONIC\n");
> -		  /* Convert the absolute timeout value to a relative
> -		     timeout.  */
> -		  rt.tv_sec = abstime->tv_sec - rt.tv_sec;
> -		  rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
> -		  if (rt.tv_nsec < 0)
> -		    {
> -		      rt.tv_nsec += 1000000000;
> -		      --rt.tv_sec;
> -		    }
> -		  /* Did we already time out?  */
> -		  if (__glibc_unlikely (rt.tv_sec < 0))
> -		    err = ETIMEDOUT;
> -		  else
> -		    err = futex_reltimed_wait_cancelable
> -			(cond->__data.__g_signals + g, 0, &rt, private);
> -		}
>  	      else
>  		{
> -		  /* Use CLOCK_REALTIME.  */
> +		  const clockid_t clockid =
> +		    ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
> +		    CLOCK_MONOTONIC : CLOCK_REALTIME;
> +
>  		  err = futex_abstimed_wait_cancelable
> -		      (cond->__data.__g_signals + g, 0, abstime, private);
> +                    (cond->__data.__g_signals + g, 0, clockid, abstime,
> +                     private);
>  		}
>  	    }

My understanding is we need to convert an absolute timeout to a relative one
on either futex_abstimed_wait_cancelable or lll_futex_clock_wait_bitset for
CLOCK_MONOTONIC.

>  
> diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
> index 270b072..d4d11cc 100644
> --- a/nptl/pthread_mutex_timedlock.c
> +++ b/nptl/pthread_mutex_timedlock.c
> @@ -266,8 +266,8 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex,
>  	  assume_other_futex_waiters |= FUTEX_WAITERS;
>  
>  	  /* Block using the futex.  */
> -	  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)

Ok.

> 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)

Ok.

> @@ -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

Ok.

> @@ -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)

Ok.

> @@ -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)

Ok.

> 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);

Ok.

>  #else
>    err = futex_abstimed_wait_cancelable (&sem->value, SEM_NWAITERS_MASK,
> -					abstime, sem->private);
> +					CLOCK_REALTIME, abstime,
> +					sem->private);
>  #endif
>  
>    return err;

Ok.

> 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

Ok.

> diff --git a/sysdeps/nptl/lowlevellock-futex.h b/sysdeps/nptl/lowlevellock-futex.h
> index 63d917d..35fcfbb 100644
> --- a/sysdeps/nptl/lowlevellock-futex.h
> +++ b/sysdeps/nptl/lowlevellock-futex.h
> @@ -43,10 +43,15 @@
>  #define lll_futex_timed_wait(futexp, val, timeout, private)             \
>    -ENOSYS
>  
> -/* 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.  */

Ok.

> diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
> index 501f993..03312d6 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:

Ok.

> @@ -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)
>      {

Ok.

> diff --git a/sysdeps/unix/sysv/linux/lowlevellock-futex.h b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> index 030a14b..ba01197 100644
> --- a/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> +++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
> @@ -82,12 +82,33 @@
>  		     __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;       \
> +        const int op =                                                  \
> +          __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, private);   \
> +                                                                        \
> +        __ret = lll_futex_syscall (6, futexp, op, val,                  \
> +                                   timeout, NULL /* Unused.  */,	\
> +                                   FUTEX_BITSET_MATCH_ANY);		\
> +      }                                                                 \
> +    else                                                                \
> +      __ret = -EINVAL;							\
> +    __ret;								\
> +  })
>  
>  #define lll_futex_wake(futexp, nr, private)                             \
>    lll_futex_syscall (4, futexp,                                         \
>
Adhemerval Zanella Netto - June 6, 2019, 12:06 p.m.
>> diff --git a/sysdeps/unix/sysv/linux/futex-internal.h b/sysdeps/unix/sysv/linux/futex-internal.h
>> index 501f993..03312d6 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);
>> +}

An addendum is to change it to return bool instead of int, since you using
with contraction checks on all patchset.
Adhemerval Zanella Netto - June 12, 2019, 7:32 p.m.
On 05/06/2019 14:52, Adhemerval Zanella wrote:

>> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
>> index 9a0f29e..7385562 100644
>> --- a/nptl/pthread_cond_wait.c
>> +++ b/nptl/pthread_cond_wait.c
>> @@ -509,35 +509,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
>>  		 values despite them being valid.  */
>>  	      if (__glibc_unlikely (abstime->tv_sec < 0))
>>  	        err = ETIMEDOUT;
>> -
>> -	      else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
>> -		{
>> -		  /* CLOCK_MONOTONIC is requested.  */
>> -		  struct timespec rt;
>> -		  if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
>> -		    __libc_fatal ("clock_gettime does not support "
>> -				  "CLOCK_MONOTONIC\n");
>> -		  /* Convert the absolute timeout value to a relative
>> -		     timeout.  */
>> -		  rt.tv_sec = abstime->tv_sec - rt.tv_sec;
>> -		  rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
>> -		  if (rt.tv_nsec < 0)
>> -		    {
>> -		      rt.tv_nsec += 1000000000;
>> -		      --rt.tv_sec;
>> -		    }
>> -		  /* Did we already time out?  */
>> -		  if (__glibc_unlikely (rt.tv_sec < 0))
>> -		    err = ETIMEDOUT;
>> -		  else
>> -		    err = futex_reltimed_wait_cancelable
>> -			(cond->__data.__g_signals + g, 0, &rt, private);
>> -		}
>>  	      else
>>  		{
>> -		  /* Use CLOCK_REALTIME.  */
>> +		  const clockid_t clockid =
>> +		    ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
>> +		    CLOCK_MONOTONIC : CLOCK_REALTIME;
>> +
>>  		  err = futex_abstimed_wait_cancelable
>> -		      (cond->__data.__g_signals + g, 0, abstime, private);
>> +                    (cond->__data.__g_signals + g, 0, clockid, abstime,
>> +                     private);
>>  		}
>>  	    }
> 
> My understanding is we need to convert an absolute timeout to a relative one
> on either futex_abstimed_wait_cancelable or lll_futex_clock_wait_bitset for
> CLOCK_MONOTONIC.

Ok rechecking the patchset, it now uses futex_abstimed_wait_cancelable instead 
of futex_reltimed_wait_cancelable, so my comment indeed does not apply.

However the naming is somewhat confusing because 'abstimed' only applies for 
clockid being CLOCK_MONOTONIC. I think we should just name the new interfaces 
as futex_timed_wait{_cancelable}.  

As a side node maybe we could simplify the futex_{abs,rel}timed_wait to call 
futex_timed_wait with expected clock on Linux implementation.
Mike Crowe - June 18, 2019, 11:44 a.m.
On Wednesday 12 June 2019 at 16:32:08 -0300, Adhemerval Zanella wrote:
> On 05/06/2019 14:52, Adhemerval Zanella wrote:
> 
> >> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
> >> index 9a0f29e..7385562 100644
> >> --- a/nptl/pthread_cond_wait.c
> >> +++ b/nptl/pthread_cond_wait.c
> >> @@ -509,35 +509,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
> >>  		 values despite them being valid.  */
> >>  	      if (__glibc_unlikely (abstime->tv_sec < 0))
> >>  	        err = ETIMEDOUT;
> >> -
> >> -	      else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
> >> -		{
> >> -		  /* CLOCK_MONOTONIC is requested.  */
> >> -		  struct timespec rt;
> >> -		  if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
> >> -		    __libc_fatal ("clock_gettime does not support "
> >> -				  "CLOCK_MONOTONIC\n");
> >> -		  /* Convert the absolute timeout value to a relative
> >> -		     timeout.  */
> >> -		  rt.tv_sec = abstime->tv_sec - rt.tv_sec;
> >> -		  rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
> >> -		  if (rt.tv_nsec < 0)
> >> -		    {
> >> -		      rt.tv_nsec += 1000000000;
> >> -		      --rt.tv_sec;
> >> -		    }
> >> -		  /* Did we already time out?  */
> >> -		  if (__glibc_unlikely (rt.tv_sec < 0))
> >> -		    err = ETIMEDOUT;
> >> -		  else
> >> -		    err = futex_reltimed_wait_cancelable
> >> -			(cond->__data.__g_signals + g, 0, &rt, private);
> >> -		}
> >>  	      else
> >>  		{
> >> -		  /* Use CLOCK_REALTIME.  */
> >> +		  const clockid_t clockid =
> >> +		    ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
> >> +		    CLOCK_MONOTONIC : CLOCK_REALTIME;
> >> +
> >>  		  err = futex_abstimed_wait_cancelable
> >> -		      (cond->__data.__g_signals + g, 0, abstime, private);
> >> +                    (cond->__data.__g_signals + g, 0, clockid, abstime,
> >> +                     private);
> >>  		}
> >>  	    }
> > 
> > My understanding is we need to convert an absolute timeout to a relative one
> > on either futex_abstimed_wait_cancelable or lll_futex_clock_wait_bitset for
> > CLOCK_MONOTONIC.
> 
> Ok rechecking the patchset, it now uses futex_abstimed_wait_cancelable instead 
> of futex_reltimed_wait_cancelable, so my comment indeed does not apply.
> 
> However the naming is somewhat confusing because 'abstimed' only applies for 
> clockid being CLOCK_MONOTONIC. I think we should just name the new interfaces 
> as futex_timed_wait{_cancelable}.

I'm afraid that I don't understand this paragraph. I don't believe that
I've added a new interface here (well, apart from the
futex_abstimed_supported_clockid function.)

futex_abstimed_wait{,_cancelable} always take an absolute timeout measured
against the specified clock. They end up calling
lll_futex_clock_wait_bitset, which passes that absolute timeout directly to
the futex syscall. It is not converted to a relative timeout at any point.

> As a side node maybe we could simplify the futex_{abs,rel}timed_wait to call
> futex_timed_wait with expected clock on Linux implementation.

This confuses me too, but that is probably due to my earlier confusion.

Thanks.

Mike.
Adhemerval Zanella Netto - June 18, 2019, 2 p.m.
On 18/06/2019 08:44, Mike Crowe wrote:
> On Wednesday 12 June 2019 at 16:32:08 -0300, Adhemerval Zanella wrote:
>> On 05/06/2019 14:52, Adhemerval Zanella wrote:
>>
>>>> diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
>>>> index 9a0f29e..7385562 100644
>>>> --- a/nptl/pthread_cond_wait.c
>>>> +++ b/nptl/pthread_cond_wait.c
>>>> @@ -509,35 +509,15 @@ __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
>>>>  		 values despite them being valid.  */
>>>>  	      if (__glibc_unlikely (abstime->tv_sec < 0))
>>>>  	        err = ETIMEDOUT;
>>>> -
>>>> -	      else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
>>>> -		{
>>>> -		  /* CLOCK_MONOTONIC is requested.  */
>>>> -		  struct timespec rt;
>>>> -		  if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
>>>> -		    __libc_fatal ("clock_gettime does not support "
>>>> -				  "CLOCK_MONOTONIC\n");
>>>> -		  /* Convert the absolute timeout value to a relative
>>>> -		     timeout.  */
>>>> -		  rt.tv_sec = abstime->tv_sec - rt.tv_sec;
>>>> -		  rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
>>>> -		  if (rt.tv_nsec < 0)
>>>> -		    {
>>>> -		      rt.tv_nsec += 1000000000;
>>>> -		      --rt.tv_sec;
>>>> -		    }
>>>> -		  /* Did we already time out?  */
>>>> -		  if (__glibc_unlikely (rt.tv_sec < 0))
>>>> -		    err = ETIMEDOUT;
>>>> -		  else
>>>> -		    err = futex_reltimed_wait_cancelable
>>>> -			(cond->__data.__g_signals + g, 0, &rt, private);
>>>> -		}
>>>>  	      else
>>>>  		{
>>>> -		  /* Use CLOCK_REALTIME.  */
>>>> +		  const clockid_t clockid =
>>>> +		    ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
>>>> +		    CLOCK_MONOTONIC : CLOCK_REALTIME;
>>>> +
>>>>  		  err = futex_abstimed_wait_cancelable
>>>> -		      (cond->__data.__g_signals + g, 0, abstime, private);
>>>> +                    (cond->__data.__g_signals + g, 0, clockid, abstime,
>>>> +                     private);
>>>>  		}
>>>>  	    }
>>>
>>> My understanding is we need to convert an absolute timeout to a relative one
>>> on either futex_abstimed_wait_cancelable or lll_futex_clock_wait_bitset for
>>> CLOCK_MONOTONIC.
>>
>> Ok rechecking the patchset, it now uses futex_abstimed_wait_cancelable instead 
>> of futex_reltimed_wait_cancelable, so my comment indeed does not apply.
>>
>> However the naming is somewhat confusing because 'abstimed' only applies for 
>> clockid being CLOCK_MONOTONIC. I think we should just name the new interfaces 
>> as futex_timed_wait{_cancelable}.
> 
> I'm afraid that I don't understand this paragraph. I don't believe that
> I've added a new interface here (well, apart from the
> futex_abstimed_supported_clockid function.)
> 
> futex_abstimed_wait{,_cancelable} always take an absolute timeout measured
> against the specified clock. They end up calling
> lll_futex_clock_wait_bitset, which passes that absolute timeout directly to
> the futex syscall. It is not converted to a relative timeout at any point.

It was a confusion from my part, sorry for the noise.  I withdrew my suggestion
here, the change looks ok thanks.

> 
>> As a side node maybe we could simplify the futex_{abs,rel}timed_wait to call
>> futex_timed_wait with expected clock on Linux implementation.
> 
> This confuses me too, but that is probably due to my earlier confusion.
> 
> Thanks.
> 
> Mike.
>

Patch

diff --git a/ChangeLog b/ChangeLog
index 53a3ae4..ff85b12 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,43 @@ 
+2019-05-27  Mike Crowe  <mac@mcrowe.com>
+
+	nptl: Add clockid parameter to futex timed wait calls
+
+	* 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): Remove
+	code to calculate relative timeout for
+	__PTHREAD_COND_CLOCK_MONOTONIC_MASK and just pass CLOCK_MONOTONIC
+	or CLOCK_REALTIME as required to futex_abstimed_wait_cancelable.
+
+	* 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
+
 2019-05-27  Florian Weimer  <fweimer@redhat.com>
 
 	* nptl/nptl-init.c: Add comment.
diff --git a/nptl/pthread_cond_wait.c b/nptl/pthread_cond_wait.c
index 9a0f29e..7385562 100644
--- a/nptl/pthread_cond_wait.c
+++ b/nptl/pthread_cond_wait.c
@@ -509,35 +509,15 @@  __pthread_cond_wait_common (pthread_cond_t *cond, pthread_mutex_t *mutex,
 		 values despite them being valid.  */
 	      if (__glibc_unlikely (abstime->tv_sec < 0))
 	        err = ETIMEDOUT;
-
-	      else if ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0)
-		{
-		  /* CLOCK_MONOTONIC is requested.  */
-		  struct timespec rt;
-		  if (__clock_gettime (CLOCK_MONOTONIC, &rt) != 0)
-		    __libc_fatal ("clock_gettime does not support "
-				  "CLOCK_MONOTONIC\n");
-		  /* Convert the absolute timeout value to a relative
-		     timeout.  */
-		  rt.tv_sec = abstime->tv_sec - rt.tv_sec;
-		  rt.tv_nsec = abstime->tv_nsec - rt.tv_nsec;
-		  if (rt.tv_nsec < 0)
-		    {
-		      rt.tv_nsec += 1000000000;
-		      --rt.tv_sec;
-		    }
-		  /* Did we already time out?  */
-		  if (__glibc_unlikely (rt.tv_sec < 0))
-		    err = ETIMEDOUT;
-		  else
-		    err = futex_reltimed_wait_cancelable
-			(cond->__data.__g_signals + g, 0, &rt, private);
-		}
 	      else
 		{
-		  /* Use CLOCK_REALTIME.  */
+		  const clockid_t clockid =
+		    ((flags & __PTHREAD_COND_CLOCK_MONOTONIC_MASK) != 0) ?
+		    CLOCK_MONOTONIC : CLOCK_REALTIME;
+
 		  err = futex_abstimed_wait_cancelable
-		      (cond->__data.__g_signals + g, 0, abstime, private);
+                    (cond->__data.__g_signals + g, 0, clockid, abstime,
+                     private);
 		}
 	    }
 
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index 270b072..d4d11cc 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -266,8 +266,8 @@  __pthread_mutex_timedlock (pthread_mutex_t *mutex,
 	  assume_other_futex_waiters |= FUTEX_WAITERS;
 
 	  /* Block using the futex.  */
-	  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 63d917d..35fcfbb 100644
--- a/sysdeps/nptl/lowlevellock-futex.h
+++ b/sysdeps/nptl/lowlevellock-futex.h
@@ -43,10 +43,15 @@ 
 #define lll_futex_timed_wait(futexp, val, timeout, private)             \
   -ENOSYS
 
-/* 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 501f993..03312d6 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 030a14b..ba01197 100644
--- a/sysdeps/unix/sysv/linux/lowlevellock-futex.h
+++ b/sysdeps/unix/sysv/linux/lowlevellock-futex.h
@@ -82,12 +82,33 @@ 
 		     __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;       \
+        const int op =                                                  \
+          __lll_private_flag (FUTEX_WAIT_BITSET | clockbit, private);   \
+                                                                        \
+        __ret = lll_futex_syscall (6, futexp, op, val,                  \
+                                   timeout, NULL /* Unused.  */,	\
+                                   FUTEX_BITSET_MATCH_ANY);		\
+      }                                                                 \
+    else                                                                \
+      __ret = -EINVAL;							\
+    __ret;								\
+  })
 
 #define lll_futex_wake(futexp, nr, private)                             \
   lll_futex_syscall (4, futexp,                                         \