hurd/hurdlock.c

   1 /* Hurd helpers for lowlevellocks.
   2    Copyright (C) 1999-2024 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    <https://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   if (clk != CLOCK_REALTIME)
  51     return EINVAL;
  52
  53   int mlsec = compute_reltime (tsp, clk);
  54   return mlsec < 0 ? KERN_TIMEDOUT : __lll_timed_wait (ptr, val, mlsec, flags);
  55 }
  56
  57 int
  58 __lll_abstimed_wait_intr (void *ptr, int val,
  59   const struct timespec *tsp, int flags, int clk)
  60 {
  61   if (clk != CLOCK_REALTIME)
  62     return EINVAL;
  63
  64   int mlsec = compute_reltime (tsp, clk);
  65   return mlsec < 0 ? KERN_TIMEDOUT : __lll_timed_wait_intr (ptr, val, mlsec, flags);
  66 }
  67
  68 int
  69 __lll_abstimed_xwait (void *ptr, int lo, int hi,
  70   const struct timespec *tsp, int flags, int clk)
  71 {
  72   if (clk != CLOCK_REALTIME)
  73     return EINVAL;
  74
  75   int mlsec = compute_reltime (tsp, clk);
  76   return mlsec < 0 ? KERN_TIMEDOUT : __lll_timed_xwait (ptr, lo, hi, mlsec,
  77                                                       flags);
  78 }
  79
  80 int
  81 __lll_abstimed_lock (void *ptr,
  82   const struct timespec *tsp, int flags, int clk)
  83 {
  84   if (clk != CLOCK_REALTIME)
  85     return EINVAL;
  86
  87   if (__lll_trylock (ptr) == 0)
  88     return 0;
  89
  90   while (1)
  91     {
  92       if (atomic_exchange_acquire ((int *)ptr, 2) == 0)
  93         return 0;
  94       else if (! valid_nanoseconds (tsp->tv_nsec))
  95         return EINVAL;
  96
  97       int mlsec = compute_reltime (tsp, clk);
  98       if (mlsec < 0 || __lll_timed_wait (ptr, 2, mlsec, flags) == KERN_TIMEDOUT)
  99         return ETIMEDOUT;
 100     }
 101 }
 102
 103 /* Robust locks.  */
 104
 105 /* Test if a given process id is still valid.  */
 106 static inline int
 107 valid_pid (int pid)
 108 {
 109   task_t task = __pid2task (pid);
 110   if (task == MACH_PORT_NULL)
 111     return 0;
 112
 113   __mach_port_deallocate (__mach_task_self (), task);
 114   return 1;
 115 }
 116
 117 /* Robust locks have currently no support from the kernel; they
 118    are simply implemented with periodic polling. When sleeping, the
 119    maximum blocking time is determined by this constant.  */
 120 #define MAX_WAIT_TIME   1500
 121
 122 int
 123 __lll_robust_lock (void *ptr, int flags)
 124 {
 125   int *iptr = (int *)ptr;
 126   int id = __getpid ();
 127   int wait_time = 25;
 128   unsigned int val;
 129
 130   /* Try to set the lock word to our PID if it's clear. Otherwise,
 131      mark it as having waiters.  */
 132   while (1)
 133     {
 134       val = *iptr;
 135       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 136         return 0;
 137       else if (atomic_compare_and_exchange_bool_acq (iptr,
 138                val | LLL_WAITERS, val) == 0)
 139         break;
 140     }
 141
 142   for (id |= LLL_WAITERS ; ; )
 143     {
 144       val = *iptr;
 145       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 146         return 0;
 147       else if (val && !valid_pid (val & LLL_OWNER_MASK))
 148         {
 149           if (atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)
 150             return EOWNERDEAD;
 151         }
 152       else
 153         {
 154           __lll_timed_wait (iptr, val, wait_time, flags);
 155           if (wait_time < MAX_WAIT_TIME)
 156             wait_time <<= 1;
 157         }
 158     }
 159 }
 160
 161 int
 162 __lll_robust_abstimed_lock (void *ptr,
 163   const struct timespec *tsp, int flags, int clk)
 164 {
 165   int *iptr = (int *)ptr;
 166   int id = __getpid ();
 167   int wait_time = 25;
 168   unsigned int val;
 169
 170   if (clk != CLOCK_REALTIME)
 171     return EINVAL;
 172
 173   while (1)
 174     {
 175       val = *iptr;
 176       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 177         return 0;
 178       else if (atomic_compare_and_exchange_bool_acq (iptr,
 179           val | LLL_WAITERS, val) == 0)
 180         break;
 181     }
 182
 183   for (id |= LLL_WAITERS ; ; )
 184     {
 185       val = *iptr;
 186       if (!val && atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 187         return 0;
 188       else if (val && !valid_pid (val & LLL_OWNER_MASK))
 189         {
 190           if (atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)
 191             return EOWNERDEAD;
 192         }
 193       else
 194         {
 195           int mlsec = compute_reltime (tsp, clk);
 196           if (mlsec < 0)
 197             return ETIMEDOUT;
 198           else if (mlsec > wait_time)
 199             mlsec = wait_time;
 200
 201           int res = __lll_timed_wait (iptr, val, mlsec, flags);
 202           if (res == KERN_TIMEDOUT)
 203             return ETIMEDOUT;
 204           else if (wait_time < MAX_WAIT_TIME)
 205             wait_time <<= 1;
 206         }
 207     }
 208 }
 209
 210 int
 211 __lll_robust_trylock (void *ptr)
 212 {
 213   int *iptr = (int *)ptr;
 214   int id = __getpid ();
 215   unsigned int val = *iptr;
 216
 217   if (!val)
 218     {
 219       if (atomic_compare_and_exchange_bool_acq (iptr, id, 0) == 0)
 220         return 0;
 221     }
 222   else if (!valid_pid (val & LLL_OWNER_MASK)
 223            && atomic_compare_and_exchange_bool_acq (iptr, id, val) == 0)
 224     return EOWNERDEAD;
 225
 226   return EBUSY;
 227 }
 228
 229 void
 230 __lll_robust_unlock (void *ptr, int flags)
 231 {
 232   unsigned int val = atomic_load_relaxed ((unsigned int *)ptr);
 233   while (1)
 234     {
 235       if (val & LLL_WAITERS)
 236         {
 237           __lll_set_wake (ptr, 0, flags);
 238           break;
 239         }
 240       else if (atomic_compare_exchange_weak_release ((unsigned int *)ptr, &val, 0))
 241         break;
 242     }
 243 }