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

Message ID 95894abea465528f7bd5f8c0971c80f0ccdd73f7.1558987219.git-series.mac@mcrowe.com
State Superseded
Headers show
Series
  • Implement POSIX-proposed _clockwait variants of existing _timedwait functions
Related show

Commit Message

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(-)

-- 
git-series 0.9.1

Comments

Adhemerval Zanella June 5, 2019, 5:52 p.m. | #1
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 June 6, 2019, 12:06 p.m. | #2
>> 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 June 12, 2019, 7:32 p.m. | #3
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. | #4
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 June 18, 2019, 2 p.m. | #5
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,                                         \