Re: [PATCH 1/3] Remove __ASSUME_FUTEX_LOCK_PI

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

Ping.

On 18/05/2016 18:57, Adhemerval Zanella wrote:
> This patch removes __ASSUME_FUTEX_LOCK_PI usage and assumes that
> kernel will correctly return if it supports or not
> futex_atomic_cmpxchg_inatomic.
> 
> Current PI mutex code already has runtime support by calling
> prio_inherit_missing and returns ENOTSUP if the futex operation fails
> at initialization (it issues a FUTEX_UNLOCK_PI futex operation).
> 
> Also, current minimum supported kernel (v3.2) will return ENOSYS if
> futex_atomic_cmpxchg_inatomic is not supported in the system:
> 
> kernel/futex.c:
> 
> 2628 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
> 2629                 u32 __user *uaddr2, u32 val2, u32 val3)
> 2630 {
> 2631         int ret = -ENOSYS, cmd = op & FUTEX_CMD_MASK;
> [...]
> 2667         case FUTEX_UNLOCK_PI:
> 2668                 if (futex_cmpxchg_enabled)
> 2669                         ret = futex_unlock_pi(uaddr, flags);
> [...]
> 2686         return ret;
> 2687 }
> 
> The futex_cmpxchg_enabled is initialized by calling cmpxchg_futex_value_locked,
> which calls futex_atomic_cmpxchg_inatomic.
> 
> For ARM futex_atomic_cmpxchg_inatomic will be either defined (if both
> CONFIG_CPU_USE_DOMAINS and CONFIG_SMP are not defined) or use the
> default generic implementation that returns ENOSYS.
> 
> For m68k is uses the default generic implementation.
> 
> For mips futex_atomic_cmpxchg_inatomic will return ENOSYS if cpu has no
> 'cpu_has_llsc' support (defined by each chip supporte inside kernel).
> 
> For sparc, 32-bit kernel will just use default generic implementation,
> while 64-bit kernel has support.
> 
> Tested on ARM (v3.8 kernel) and x86_64.
> 
> 	* nptl/pthread_mutex_init.c [__ASSUME_FUTEX_LOCK_PI]
> 	(prio_inherit_missing): Remove define.
> 	* sysdeps/unix/sysv/linux/arm/kernel-features.h
> 	(__ASSUME_FUTEX_LOCK_PI): Likewise.
> 	* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_FUTEX_LOCK_PI):
> 	Likewise.
> 	* sysdeps/unix/sysv/linux/m68k/kernel-features.h
> 	(__ASSUME_FUTEX_LOCK_PI): Likewise.
> 	* sysdeps/unix/sysv/linux/mips/kernel-features.h
> 	(__ASSUME_FUTEX_LOCK_PI): Likewise.
> 	* sysdeps/unix/sysv/linux/sparc/kernel-features.h
> 	(__ASSUME_FUTEX_LOCK_PI): Likewise.
> ---
>  ChangeLog                                       | 15 +++++++++++++++
>  nptl/pthread_mutex_init.c                       |  3 ---
>  sysdeps/unix/sysv/linux/arm/kernel-features.h   |  1 -
>  sysdeps/unix/sysv/linux/kernel-features.h       |  4 ----
>  sysdeps/unix/sysv/linux/m68k/kernel-features.h  |  1 -
>  sysdeps/unix/sysv/linux/mips/kernel-features.h  |  1 -
>  sysdeps/unix/sysv/linux/sparc/kernel-features.h |  1 -
>  7 files changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/nptl/pthread_mutex_init.c b/nptl/pthread_mutex_init.c
> index 71ac7bc..6e5acb6 100644
> --- a/nptl/pthread_mutex_init.c
> +++ b/nptl/pthread_mutex_init.c
> @@ -37,7 +37,6 @@ static bool
>  prio_inherit_missing (void)
>  {
>  #ifdef __NR_futex
> -# ifndef __ASSUME_FUTEX_LOCK_PI
>    static int tpi_supported;
>    if (__glibc_unlikely (tpi_supported == 0))
>      {
> @@ -48,8 +47,6 @@ prio_inherit_missing (void)
>        tpi_supported = INTERNAL_SYSCALL_ERRNO (ret, err) == ENOSYS ? -1 : 1;
>      }
>    return __glibc_unlikely (tpi_supported < 0);
> -# endif
> -  return false;
>  #endif
>    return true;
>  }
> diff --git a/sysdeps/unix/sysv/linux/arm/kernel-features.h b/sysdeps/unix/sysv/linux/arm/kernel-features.h
> index 0a9ed77..6ca607e 100644
> --- a/sysdeps/unix/sysv/linux/arm/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/arm/kernel-features.h
> @@ -23,7 +23,6 @@
>     futex_atomic_cmpxchg_inatomic, depending on kernel
>     configuration.  */
>  #if __LINUX_KERNEL_VERSION < 0x030E03
> -# undef __ASSUME_FUTEX_LOCK_PI
>  # undef __ASSUME_REQUEUE_PI
>  # undef __ASSUME_SET_ROBUST_LIST
>  #endif
> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 5a1b204..43b72b1 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -64,10 +64,6 @@
>     configurations).  */
>  #define __ASSUME_SET_ROBUST_LIST	1
>  
> -/* Support for PI futexes was added in 2.6.18 (but some architectures
> -   lack futex_atomic_cmpxchg_inatomic in some configurations).  */
> -#define __ASSUME_FUTEX_LOCK_PI	1
> -
>  /* Support for private futexes was added in 2.6.22.  */
>  #define __ASSUME_PRIVATE_FUTEX	1
>  
> diff --git a/sysdeps/unix/sysv/linux/m68k/kernel-features.h b/sysdeps/unix/sysv/linux/m68k/kernel-features.h
> index 646bc4b..9e7f0e1 100644
> --- a/sysdeps/unix/sysv/linux/m68k/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/m68k/kernel-features.h
> @@ -51,7 +51,6 @@
>  
>  /* No support for PI futexes or robust mutexes before 3.10 for m68k.  */
>  #if __LINUX_KERNEL_VERSION < 0x030a00
> -# undef __ASSUME_FUTEX_LOCK_PI
>  # undef __ASSUME_REQUEUE_PI
>  # undef __ASSUME_SET_ROBUST_LIST
>  #endif
> diff --git a/sysdeps/unix/sysv/linux/mips/kernel-features.h b/sysdeps/unix/sysv/linux/mips/kernel-features.h
> index e831645..09d5ece 100644
> --- a/sysdeps/unix/sysv/linux/mips/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/mips/kernel-features.h
> @@ -24,7 +24,6 @@
>  /* The MIPS kernel does not support futex_atomic_cmpxchg_inatomic if
>     emulating LL/SC.  */
>  #if __mips == 1 || defined _MIPS_ARCH_R5900
> -# undef __ASSUME_FUTEX_LOCK_PI
>  # undef __ASSUME_REQUEUE_PI
>  # undef __ASSUME_SET_ROBUST_LIST
>  #endif
> diff --git a/sysdeps/unix/sysv/linux/sparc/kernel-features.h b/sysdeps/unix/sysv/linux/sparc/kernel-features.h
> index 386f230..69c9c7c 100644
> --- a/sysdeps/unix/sysv/linux/sparc/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/sparc/kernel-features.h
> @@ -34,7 +34,6 @@
>  /* 32-bit SPARC kernels do not support
>     futex_atomic_cmpxchg_inatomic.  */
>  #if !defined __arch64__ && !defined __sparc_v9__
> -# undef __ASSUME_FUTEX_LOCK_PI
>  # undef __ASSUME_REQUEUE_PI
>  # undef __ASSUME_SET_ROBUST_LIST
>  #endif
>