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

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

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,                                         \
>