Re: [PATCH 18/18] linux: Only use 64-bit syscall if required for clock_nanosleep

[Lukasz Majewski <lukma@denx.de>]

[-- Attachment #1: Type: text/plain, Size: 6999 bytes --]

Hi Adhemerval,

> For !__ASSUME_TIME64_SYSCALLS there is no need to issue a 64-bit
> syscall if the provided timeout fits in a 32-bit one.  The 64-bit
> usage should be rare since the timeout is a relative one.

I'm not sure if the above description is correct.

As fair as I understand this patch set - we check if timeout fits into
32-bit if:

- We want to use legacy (32 bit) syscall when __ASSUME_TIME64_SYSCALLS
  is not defined to avoid calling syscalls twice.

The problem with relative 64 bit timeouts will be apparent after we
pass Y2038 year threshold. 

> 
> Checked on i686-linux-gnu on a 4.15 kernel and on a 5.11 kernel
> (with and without --enable-kernel=5.1) and on x86_64-linux-gnu.
> ---
>  sysdeps/unix/sysv/linux/clock_nanosleep.c | 47
> +++++++++++++---------- time/Makefile                             |
> 9 +++++ time/tst-clock_nanosleep.c                | 40
> +++++++++++-------- 3 files changed, 60 insertions(+), 36 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c
> b/sysdeps/unix/sysv/linux/clock_nanosleep.c index
> 007f1736cb..46b0f1e269 100644 ---
> a/sysdeps/unix/sysv/linux/clock_nanosleep.c +++
> b/sysdeps/unix/sysv/linux/clock_nanosleep.c @@ -27,8 +27,9 @@
>  /* We can simply use the syscall.  The CPU clocks are not supported
>     with this function.  */
>  int
> -__clock_nanosleep_time64 (clockid_t clock_id, int flags, const
> struct __timespec64 *req,
> -                          struct __timespec64 *rem)
> +__clock_nanosleep_time64 (clockid_t clock_id, int flags,
> +			  const struct __timespec64 *req,
> +			  struct __timespec64 *rem)
>  {
>    if (clock_id == CLOCK_THREAD_CPUTIME_ID)
>      return EINVAL;
> @@ -37,33 +38,37 @@ __clock_nanosleep_time64 (clockid_t clock_id, int
> flags, const struct __timespec 
>    /* If the call is interrupted by a signal handler or encounters an
> error, it returns a positive value similar to errno.  */
> +
>  #ifndef __NR_clock_nanosleep_time64
>  # define __NR_clock_nanosleep_time64 __NR_clock_nanosleep
>  #endif
> -  int r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id,
> -				   flags, req, rem);
> -
> -#ifndef __ASSUME_TIME64_SYSCALLS
> -  if (r == 0 || r != -ENOSYS)
> -    return -r;
>  
> -  if (! in_time_t_range (req->tv_sec))
> +  int r;
> +#ifdef __ASSUME_TIME64_SYSCALLS
> +  r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id,
> flags, req,
> +			       rem);
> +#else
> +  bool is32bit = in_time_t_range (req->tv_sec);
> +  if (!is32bit)
>      {
> -      __set_errno (EOVERFLOW);
> -      return -1;
> +      r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id,
> flags,
> +				   req, rem);
> +      if (r == -ENOSYS)
> +	r = -EOVERFLOW;
>      }
> -
> -  struct timespec tr32;
> -  struct timespec ts32 = valid_timespec64_to_timespec (*req);
> -  r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep, clock_id, flags,
> -                               &ts32, &tr32);
> -  if (INTERNAL_SYSCALL_ERROR_P (r))
> +  else
>      {
> -      if (r == -EINTR && rem != NULL && (flags & TIMER_ABSTIME) == 0)
> -	*rem = valid_timespec_to_timespec64 (tr32);
> +      struct timespec tr32;
> +      struct timespec ts32 = valid_timespec64_to_timespec (*req);
> +      r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep, clock_id, flags,
> &ts32,
> +				   &tr32);
> +      if (INTERNAL_SYSCALL_ERROR_P (r))
> +	{
> +	  if (r == -EINTR && rem != NULL && (flags & TIMER_ABSTIME)
> == 0)
> +	    *rem = valid_timespec_to_timespec64 (tr32);
> +	}
>      }
> -#endif /* __ASSUME_TIME64_SYSCALLS */
> -
> +#endif
>    return -r;
>  }
>  
> diff --git a/time/Makefile b/time/Makefile
> index c84bd5d3ec..0bea84966c 100644
> --- a/time/Makefile
> +++ b/time/Makefile
> @@ -86,6 +86,15 @@ $(objpfx)tst-strftime2.out: $(gen-locales)
>  $(objpfx)tst-strftime3.out: $(gen-locales)
>  endif
>  
> +ifeq (yes,$(build-shared))
> +librt = $(common-objpfx)rt/librt.so
> +else
> +librt = $(common-objpfx)rt/librt.a
> +endif
> +
> +$(objpfx)tst-clock_nanosleep: $(librt)
> +$(objpfx)tst-clock_nanosleep-time64: $(librt)
> +
>  tz-cflags = -DTZDIR='"$(zonedir)"' \
>  	    -DTZDEFAULT='"$(localtime-file)"' \
>  	    -DTZDEFRULES='"$(posixrules-file)"'
> diff --git a/time/tst-clock_nanosleep.c b/time/tst-clock_nanosleep.c
> index 47537435c1..a5a7f9430a 100644
> --- a/time/tst-clock_nanosleep.c
> +++ b/time/tst-clock_nanosleep.c
> @@ -20,38 +20,48 @@
>  #include <unistd.h>
>  #include <sys/time.h>
>  #include <time.h>
> -
> +#include <intprops.h>
> +#include <support/support.h>
> +#include <support/check.h>
>  
>  /* Test that clock_nanosleep() does sleep.  */
> -static int
> -do_test (void)
> +static void
> +clock_nanosleep_test (void)
>  {
>    /* Current time.  */
>    struct timeval tv1;
> -  (void) gettimeofday (&tv1, NULL);
> +  gettimeofday (&tv1, NULL);
>  
> -  struct timespec ts;
> -  ts.tv_sec = 1;
> -  ts.tv_nsec = 0;
> +  struct timespec ts = { 1, 0 };
>    TEMP_FAILURE_RETRY (clock_nanosleep (CLOCK_REALTIME, 0, &ts, &ts));
>  
>    /* At least one second must have passed.  */
>    struct timeval tv2;
> -  (void) gettimeofday (&tv2, NULL);
> +  gettimeofday (&tv2, NULL);
>  
>    tv2.tv_sec -= tv1.tv_sec;
>    tv2.tv_usec -= tv1.tv_usec;
>    if (tv2.tv_usec < 0)
>      --tv2.tv_sec;
>  
> -  if (tv2.tv_sec < 1)
> -    {
> -      puts ("clock_nanosleep didn't sleep long enough");
> -      return 1;
> -    }
> +  TEST_VERIFY (tv2.tv_sec >= 1);
> +}
> +
> +static void
> +clock_nanosleep_large_timeout (void)
> +{

Please correct me if I'm wrong:

> +  support_create_timer (0, 100000000, false, NULL);

You create timer with 100ms timeout

> +  struct timespec ts = { TYPE_MAXIMUM (time_t), 0 };

ts is created to have maximal value for time_t seconds.

> +  int r = clock_nanosleep (CLOCK_REALTIME, 0, &ts, NULL);

The clock_nanosleep is called (64 or 32 bit version - with proper
in-glibc aliasing).

> +  TEST_VERIFY (r == EINTR || r == EOVERFLOW);

We check if:

- return is EOVERFLOW - this means that we want to use 64 bit time on
  machine which is only supporting 64 bit time.

- return is EINTR - as the timer's (introduced in the earlier patch in
  this set) alarm triggers. Am I right that this check is to find out
  if the syscall is correctly executed by the kernel?

  Or is there any other issue?

> +}
>  
> +static int
> +do_test (void)
> +{
> +  clock_nanosleep_test ();
> +  clock_nanosleep_large_timeout ();
>    return 0;
>  }
>  
> -#define TEST_FUNCTION do_test ()
> -#include "../test-skeleton.c"
> +#include <support/test-driver.c>



Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]