hurd/hurdlock.c

   1 /* Hurd helpers for lowlevellocks.
   2    Copyright (C) 1999-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include "hurdlock.h"
  20 #include <hurd.h>
  21 #include <hurd/hurd.h>
  22 #include <time.h>
  23 #include <errno.h>
  24 #include <unistd.h>
  25
  26 /* Convert an absolute timeout in nanoseconds to a relative
  27    timeout in milliseconds.  */
  28 static inline int __attribute__ ((gnu_inline))
  29 compute_reltime (const struct timespec *abstime, clockid_t clk)
  30 {
  31   struct timespec ts;
  32   __clock_gettime (clk, &ts);
  33
  34   ts.tv_sec = abstime->tv_sec - ts.tv_sec;
  35   ts.tv_nsec = abstime->tv_nsec - ts.tv_nsec;
  36
  37   if (ts.tv_nsec < 0)
  38     {
  39       --ts.tv_sec;
  40       ts.tv_nsec += 1000000000;
  41     }
  42
  43   return ts.tv_sec < 0 ? -1 : (int)(ts.tv_sec * 1000 + ts.tv_nsec / 1000000);
  44 }
  45
  46 int
  47 __lll_abstimed_wait (void *ptr, int val,
  48   const struct timespec *tsp, int flags, int clk)
  49 {
  50   int mlsec = compute_reltime (tsp, clk);
  51   return mlsec < 0 ? KERN_TIMEDOUT : lll_timed_wait (ptr, val, mlsec, flags);
  52 }
  53
  54 int
  55 __lll_abstimed_xwait (void *ptr, int lo, int hi,
  56   const struct timespec *tsp, int flags, int clk)
  57 {
  58   int mlsec = compute_reltime (tsp, clk);
  59   return mlsec < 0 ? KERN_TIMEDOUT : lll_timed_xwait (ptr, lo, hi, mlsec,
  60                                                       flags);
  61 }
  62
  63 int
  64 __lll_abstimed_lock (void *ptr,
  65   const struct timespec *tsp, int flags, int clk)
  66 {
  67   if (lll_trylock (ptr) == 0)
  68     return 0;
  69
  70   while (1)
  71     {
  72       if (atomic_exchange_acq ((int *)ptr, 2) == 0)
  73         return 0;
  74       else if (tsp->tv_nsec < 0 || tsp->tv_nsec >= 1000000000)
  75         return EINVAL;
  76
  77       int mlsec = compute_reltime (tsp, clk);
  78       if (mlsec < 0 || lll_timed_wait (ptr, 2, mlsec, flags) == KERN_TIMEDOUT)
  79         return ETIMEDOUT;
  80     }
  81 }
  82
  83 /* Robust locks.  */
  84
  85 /* Test if a given process id is still valid.  */
  86 static inline int
  87 valid_pid (int pid)
  88 {
  89   task_t task = __pid2task (pid);
  90   if (task == MACH_PORT_NULL)
  91     return 0;
  92
  93   __mach_port_deallocate (__mach_task_self (), task);
  94   return 1;
  95 }
  96
  97 /* Robust locks have currently no support from the kernel; they
  98    are simply implemented with periodic polling. When sleeping, the
  99    maximum blocking time is determined by this constant.  */
 100 #define MAX_WAIT_TIME   1500
 101
 102 int
 103 __lll_robust_lock (void *ptr, int flags)
 104 {
 105   int *iptr = (int *)ptr;
 106   int id = __getpid ();
 107   int wait_time = 25;
 108   unsigned int val;
 109
 110   /* Try to set the lock word to our PID if it's clear. Otherwise,
 111      mark it as having waiters.  */
 112   while (1)
 113     {
 114       val = *iptr;
 115       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 116         return 0;
 117       else if (atomic_compare_and_exchange_bool_acq (iptr,
 118                val | LLL_WAITERS, val) == 0)
 119         break;
 120     }
 121
 122   for (id |= LLL_WAITERS ; ; )
 123     {
 124       val = *iptr;
 125       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 126         return 0;
 127       else if (val && !valid_pid (val & LLL_OWNER_MASK))
 128         {
 129           if (atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)
 130             return EOWNERDEAD;
 131         }
 132       else
 133         {
 134           lll_timed_wait (iptr, val, wait_time, flags);
 135           if (wait_time < MAX_WAIT_TIME)
 136             wait_time <<= 1;
 137         }
 138     }
 139 }
 140
 141 int
 142 __lll_robust_abstimed_lock (void *ptr,
 143   const struct timespec *tsp, int flags, int clk)
 144 {
 145   int *iptr = (int *)ptr;
 146   int id = __getpid ();
 147   int wait_time = 25;
 148   unsigned int val;
 149
 150   while (1)
 151     {
 152       val = *iptr;
 153       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 154         return 0;
 155       else if (atomic_compare_and_exchange_bool_acq (iptr,
 156           val | LLL_WAITERS, val) == 0)
 157         break;
 158     }
 159
 160   for (id |= LLL_WAITERS ; ; )
 161     {
 162       val = *iptr;
 163       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 164         return 0;
 165       else if (val && !valid_pid (val & LLL_OWNER_MASK))
 166         {
 167           if (atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)
 168             return EOWNERDEAD;
 169         }
 170       else
 171         {
 172           int mlsec = compute_reltime (tsp, clk);
 173           if (mlsec < 0)
 174             return ETIMEDOUT;
 175           else if (mlsec > wait_time)
 176             mlsec = wait_time;
 177
 178           int res = lll_timed_wait (iptr, val, mlsec, flags);
 179           if (res == KERN_TIMEDOUT)
 180             return ETIMEDOUT;
 181           else if (wait_time < MAX_WAIT_TIME)
 182             wait_time <<= 1;
 183         }
 184     }
 185 }
 186
 187 int
 188 __lll_robust_trylock (void *ptr)
 189 {
 190   int *iptr = (int *)ptr;
 191   int id = __getpid ();
 192   unsigned int val = *iptr;
 193
 194   if (!val)
 195     {
 196       if (atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 197         return 0;
 198     }
 199   else if (!valid_pid (val & LLL_OWNER_MASK)
 200            && atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)
 201     return EOWNERDEAD;
 202
 203   return EBUSY;
 204 }
 205
 206 void
 207 __lll_robust_unlock (void *ptr, int flags)
 208 {
 209   unsigned int val = atomic_load_relaxed ((unsigned int *)ptr);
 210   while (1)
 211     {
 212       if (val & LLL_WAITERS)
 213         {
 214           lll_set_wake (ptr, 0, flags);
 215           break;
 216         }
 217       else if (atomic_compare_exchange_weak_release ((unsigned int *)ptr, &val, 0))
 218         break;
 219     }
 220 }