Re: [PATCH v4] sysdeps/nanosleep: Use clock_nanosleep_time64 if avaliable

[Alistair Francis <alistair23 at gmail dot com>]

On Wed, Nov 6, 2019 at 2:11 AM Lukasz Majewski <lukma@denx.de> wrote:
>
> Hi Alistair, Joseph,
>
> > The nanosleep syscall is not supported on newer 32-bit platforms (such
> > as RV32). To fix this issue let's use clock_nanosleep_time64 if it is
> > avaliable.
> >
> > Let's use CLOCK_REALTIME when calling clock_nanosleep_time64 as the
> > Linux specification says:
> >   "POSIX.1 specifies that nanosleep() should measure time against the
> >    CLOCK_REALTIME clock. However, Linux measures the time using the
> >    CLOCK_MONOTONIC clock. This probably does not matter, since the
> > POSIX.1 specification for clock_settime(2) says that discontinuous
> > changes in CLOCK_REALTIME should not affect nanosleep()"
> >
> > Let's also expose __clock_nanosleep internally to avoid code
> > duplication.
> > ---
> > This was patch was runtime tested with RV32 and RV64
> > It was build tested using the ./scripts/build-many-glibcs.py script.
> >
> > I am currently running:
> > $ make ; make install ; make check
> > tests on native ARM (32-bit) with the following three confiugrations:
> >  - 4.19 Kernel and 4.19 Headers
> >  - 5.2 Kernel and 4.19 Headers
> >  - 5.2 Kernel and 5.2 Headers
> > I should have the results tomorrow.
> >
> > v4:
> >  - Rebase on master
> >  - Use __clock_nanosleep to avoid duplicate implementations
> >  - Fix the error handling when a syscall fails
> > v2:
> >  - Explicitly include `#include <kernel-features.h>`
> >
> >  include/time.h                            | 23 ++++++++
> >  nptl/thrd_sleep.c                         | 25 ++++-----
> >  sysdeps/unix/sysv/linux/Versions          |  1 +
> >  sysdeps/unix/sysv/linux/clock_nanosleep.c | 68
> > +++++++++++++++++++++-- sysdeps/unix/sysv/linux/nanosleep.c       |
> > 13 +++-- 5 files changed, 106 insertions(+), 24 deletions(-)
> >
> > diff --git a/include/time.h b/include/time.h
> > index 8ac58e891b5..e0974309726 100644
> > --- a/include/time.h
> > +++ b/include/time.h
> > @@ -184,6 +184,9 @@ extern struct tm *__tz_convert (__time64_t timer,
> > int use_localtime, extern int __nanosleep (const struct timespec
> > *__requested_time, struct timespec *__remaining);
> >  hidden_proto (__nanosleep)
> > +extern int __clock_nanosleep (clockid_t clock_id, int flags,
> > +                              const struct timespec *req, struct
> > timespec *rem); +libc_hidden_proto (__clock_nanosleep)
> >  extern int __getdate_r (const char *__string, struct tm *__resbufp)
> >    attribute_hidden;
> >
> > @@ -206,6 +209,26 @@ libc_hidden_proto (__difftime64)
> >
> >  extern double __difftime (time_t time1, time_t time0);
> >
> > +#if __TIMESIZE == 64
> > +# define __thrd_sleep_time64 thrd_sleep
> > +# define __clock_nanosleep_time64 __clock_nanosleep
> > +# define __nanosleep_time64 __nanosleep
> > +# define __nanosleep_nocancel_time64 __nanosleep_nocancel
> > +#else
> > +extern int __thrd_sleep_time64 (const struct __timespec64*
> > time_point,
> > +                                struct __timespec64* remaining);
> > +libc_hidden_proto (__thrd_sleep_time64)
> > +extern int __clock_nanosleep_time64 (clockid_t clock_id,
> > +                                     int flags, const struct
> > __timespec64 *req,
> > +                                     struct __timespec64 *rem);
> > +libc_hidden_proto (__clock_nanosleep_time64)
> > +extern int __nanosleep_time64 (const struct __timespec64
> > *requested_time,
> > +                                struct __timespec64 *remaining);
> > +libc_hidden_proto (__nanosleep_time64)
> > +extern int __nanosleep_nocancel_time64 (const struct __timespec64
> > *requested_time,
> > +                                        struct __timespec64
> > *remaining); +libc_hidden_proto (__nanosleep_nocancel_time64)
> > +#endif
> >
> >  /* Use in the clock_* functions.  Size of the field representing the
> >     actual clock ID.  */
> > diff --git a/nptl/thrd_sleep.c b/nptl/thrd_sleep.c
> > index 2e185dd748e..c865f815eea 100644
> > --- a/nptl/thrd_sleep.c
> > +++ b/nptl/thrd_sleep.c
> > @@ -17,23 +17,18 @@
> >     <https://www.gnu.org/licenses/>.  */
> >
> >  #include <time.h>
> > -#include <sysdep-cancel.h>
> > -
> > -#include "thrd_priv.h"
> > +#include <errno.h>
> >
> >  int
> >  thrd_sleep (const struct timespec* time_point, struct timespec*
> > remaining) {
> > -  INTERNAL_SYSCALL_DECL (err);
> > -  int ret = INTERNAL_SYSCALL_CANCEL (nanosleep, err, time_point,
> > remaining);
> > -  if (INTERNAL_SYSCALL_ERROR_P (ret, err))
> > -    {
> > -      /* C11 states thrd_sleep function returns -1 if it has been
> > interrupted
> > -      by a signal, or a negative value if it fails.  */
> > -      ret = INTERNAL_SYSCALL_ERRNO (ret, err);
> > -      if (ret == EINTR)
> > -     return -1;
> > -      return -2;
> > -    }
> > -  return 0;
> > +  int ret = __clock_nanosleep (CLOCK_REALTIME, 0, time_point,
> > remaining);
>
> Maybe this is a bit off topic (generic question to 64 bit time support)
> - but I'm wondering if we shall not use __clock_nanosleep_time64 here
> just from the outset?
>
> With using __clock_nanosleep() as the internal function, the
> architectures with __TIMESIZE != 64 (e.g. ARM32 bit) will not benefit
> from having internal glibc support for 64 bit time representation (as
> their __clock_nanosleep version uses 32 bit to represent time).
>
> Of course we can stick to __clock_nanosleep, but then those functions
> would need to be aliased or (better) renamed in the code before Y2038.
>
> The same situation is with e.g. internal usage of __clock_settime.
>
> > +  /* C11 states thrd_sleep function returns -1 if it has been
> > interrupted
> > +     by a signal, or a negative value if it fails.  */
> > +  switch (ret)
> > +  {
> > +     case 0:      return 0;
> > +     case EINTR:  return -1;
> > +     default:     return -2;
> > +  }
> >  }
> > diff --git a/sysdeps/unix/sysv/linux/Versions
> > b/sysdeps/unix/sysv/linux/Versions index d385085c611..475abb50040
> > 100644 --- a/sysdeps/unix/sysv/linux/Versions
> > +++ b/sysdeps/unix/sysv/linux/Versions
> > @@ -187,5 +187,6 @@ libc {
> >      __sigtimedwait;
> >      # functions used by nscd
> >      __netlink_assert_response;
> > +    __clock_nanosleep;
> >    }
> >  }
> > diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c
> > b/sysdeps/unix/sysv/linux/clock_nanosleep.c index
> > 1f240b8720a..13ea9c6f802 100644 ---
> > a/sysdeps/unix/sysv/linux/clock_nanosleep.c +++
> > b/sysdeps/unix/sysv/linux/clock_nanosleep.c @@ -16,6 +16,7 @@
> >     <https://www.gnu.org/licenses/>.  */
> >
> >  #include <time.h>
> > +#include <kernel-features.h>
> >  #include <errno.h>
> >
> >  #include <sysdep-cancel.h>
> > @@ -26,9 +27,11 @@
> >  /* We can simply use the syscall.  The CPU clocks are not supported
> >     with this function.  */
> >  int
> > -__clock_nanosleep (clockid_t clock_id, int flags, const struct
> > timespec *req,
> > -                struct timespec *rem)
> > +__clock_nanosleep_time64 (clockid_t clock_id, int flags, const
>    ^^^^^^^^^^^^^^^^^ - just an open question - shall we have the naming
>    convention (for this function) following the new syscalls names or
>    use e.g. __clock_nanosleep64() ?
>
> > struct __timespec64 *req,
> > +                          struct __timespec64 *rem)
> >  {
> > +  int r = -1;
> > +
> >    if (clock_id == CLOCK_THREAD_CPUTIME_ID)
> >      return EINVAL;
> >    if (clock_id == CLOCK_PROCESS_CPUTIME_ID)
> > @@ -37,12 +40,67 @@ __clock_nanosleep (clockid_t clock_id, int flags,
> > const struct timespec *req, /* If the call is interrupted by a signal
> > handler or encounters an error, it returns a positive value similar
> > to errno.  */ INTERNAL_SYSCALL_DECL (err);
> > -  int r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep, err, clock_id,
> > flags,
> > -                                req, rem);
> > +
> > +#ifdef __ASSUME_TIME64_SYSCALLS
> > +# ifndef __NR_clock_nanosleep_time64
> > +#  define __NR_clock_nanosleep_time64 __NR_clock_nanosleep
> > +# endif
> > +  r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, err, clock_id,
> > +                               flags, req, rem);
> > +#else
> > +# ifdef __NR_clock_nanosleep_time64
> > +  long int ret_64;
>
> I think that 'int ret;' would be a bit better.
>
> the clock_nanosleep syscall [1] returns int.

I have changed this to int.

>
> > +
> > +  ret_64 = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, err,
> > clock_id,
> > +                                    flags, req, rem);
> > +
> > +  if (ret_64 == 0 || errno != ENOSYS)
> > +    {
> > +      return (INTERNAL_SYSCALL_ERROR_P (ret_64, err)
> > +              ? INTERNAL_SYSCALL_ERRNO (ret_64, err) : 0);
> > +    }
> > +# endif /* __NR_clock_nanosleep_time64 */
> > +  struct timespec ts32, tr32;
> > +
> > +  if (! in_time_t_range (req->tv_sec))
> > +    {
> > +      __set_errno (EOVERFLOW);
> > +      return -1;
> > +    }
> > +
> > +  ts32 = valid_timespec64_to_timespec (*req);
>
> The man pages for clock_nanosleep (e.g. [2], [3]) do not mention about
> the possibility to have *req equal to NULL, hence I do assume that we
> don't need to do it here as well...

I really don't like accessing a pointer without first checking it.
__clock_nanosleep is going to be called from inside glibc so I think
it makes sense to keep the check in.

If people prefer that I remove it I can.

>
> > +  r =  INTERNAL_SYSCALL_CANCEL (clock_nanosleep, err, &ts32, &tr32);

^

This line is broken. I am not passing in flags or clock_id and it
causes test failures. I will re-test and send a new version.

Alistair

> > +
> > +  if ((r == 0 || errno != ENOSYS) && rem)
> > +    *rem = valid_timespec_to_timespec64 (tr32);
> > +#endif /* __ASSUME_TIME64_SYSCALLS */
> > +
> >    return (INTERNAL_SYSCALL_ERROR_P (r, err)
> > -       ? INTERNAL_SYSCALL_ERRNO (r, err) : 0);
> > +          ? INTERNAL_SYSCALL_ERRNO (r, err) : 0);
> >  }
> >
> > +#if __TIMESIZE != 64
> > +int
> > +__clock_nanosleep (clockid_t clock_id, int flags, const struct
> > timespec *req,
> > +                   struct timespec *rem)
> > +{
> > +  int r;
> > +  struct __timespec64 treq64, trem64;
> > +
> > +  treq64 = valid_timespec_to_timespec64 (*req);
> > +  r = __clock_nanosleep_time64 (clock_id, flags, &treq64, &trem64);
> > +
> > +  if (r == 0 || errno != ENOSYS)
> > +    {
> > +      if (rem)
> > +        *rem = valid_timespec64_to_timespec (trem64);
> > +    }
> > +
> > +  return r;
> > +}
> > +#endif
> > +libc_hidden_def (__clock_nanosleep)
> > +
> >  versioned_symbol (libc, __clock_nanosleep, clock_nanosleep,
> > GLIBC_2_17); /* clock_nanosleep moved to libc in version 2.17;
> >     old binaries may expect the symbol version it had in librt.  */
> > diff --git a/sysdeps/unix/sysv/linux/nanosleep.c
> > b/sysdeps/unix/sysv/linux/nanosleep.c index 6787909248f..30cc26909a7
> > 100644 --- a/sysdeps/unix/sysv/linux/nanosleep.c
> > +++ b/sysdeps/unix/sysv/linux/nanosleep.c
> > @@ -17,15 +17,20 @@
> >     <https://www.gnu.org/licenses/>.  */
> >
> >  #include <time.h>
> > -#include <sysdep-cancel.h>
> > -#include <not-cancel.h>
> > +#include <errno.h>
> >
> >  /* Pause execution for a number of nanoseconds.  */
> >  int
> >  __nanosleep (const struct timespec *requested_time,
> > -          struct timespec *remaining)
> > +             struct timespec *remaining)
> >  {
> > -  return SYSCALL_CANCEL (nanosleep, requested_time, remaining);
> > +  int ret = __clock_nanosleep (CLOCK_REALTIME, 0, requested_time,
> > remaining);
> > +  if (ret != 0)
> > +    {
> > +      __set_errno (ret);
> > +      return -1;
> > +    }
> > +  return ret;
> >  }
> >  hidden_def (__nanosleep)
> >  weak_alias (__nanosleep, nanosleep)
>
>
> Links:
>
> [1] -
> https://elixir.bootlin.com/linux/v5.4-rc5/source/kernel/time/posix-timers.c#L1230
>
> [2] - http://man7.org/linux/man-pages/man2/nanosleep.2.html
>
> [3] - https://linux.die.net/man/3/clock_nanosleep
>
> 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