nptl/tst-rwlock20.c

   1 /* Test program for a read-phase / write-phase explicit hand-over.
   2    Copyright (C) 2017-2023 Free Software Foundation, Inc.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If
  16    not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <error.h>
  20 #include <pthread.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <unistd.h>
  24 #include <stdint.h>
  25 #include <time.h>
  26 #include <atomic.h>
  27 #include <support/xthread.h>
  28
  29 /* We really want to set threads to 2 to reproduce this issue. The goal
  30    is to have one primary writer and a single reader, and to hit the
  31    bug that happens in the interleaving of those two phase transitions.
  32    However, on most hardware, adding a second writer seems to help the
  33    interleaving happen slightly more often, say 20% of the time.  On a
  34    16 core ppc64 machine this fails 100% of the time with an unpatched
  35    glibc.  On a 8 core x86_64 machine this fails ~93% of the time, but
  36    it doesn't fail at all on a 4 core system, so having available
  37    unloaded cores makes a big difference in reproducibility.  On an 8
  38    core qemu/kvm guest the reproducer reliability drops to ~10%.  */
  39 #define THREADS 3
  40
  41 #define KIND PTHREAD_RWLOCK_PREFER_READER_NP
  42
  43 static pthread_rwlock_t lock;
  44 static int done = 0;
  45
  46 static void*
  47 tf (void* arg)
  48 {
  49   while (atomic_load_relaxed (&done) == 0)
  50     {
  51       int rcnt = 0;
  52       int wcnt = 100;
  53       if ((uintptr_t) arg == 0)
  54         {
  55           rcnt = 1;
  56           wcnt = 1;
  57         }
  58
  59       do
  60         {
  61           if (wcnt)
  62             {
  63               xpthread_rwlock_wrlock (&lock);
  64               xpthread_rwlock_unlock (&lock);
  65               wcnt--;
  66           }
  67           if (rcnt)
  68             {
  69               xpthread_rwlock_rdlock (&lock);
  70               xpthread_rwlock_unlock (&lock);
  71               rcnt--;
  72           }
  73         }
  74       while ((atomic_load_relaxed (&done) == 0) && (rcnt + wcnt > 0));
  75
  76     }
  77     return NULL;
  78 }
  79
  80
  81
  82 static int
  83 do_test (void)
  84 {
  85   pthread_t thr[THREADS];
  86   int n;
  87   pthread_rwlockattr_t attr;
  88
  89   xpthread_rwlockattr_init (&attr);
  90   xpthread_rwlockattr_setkind_np (&attr, KIND);
  91
  92   xpthread_rwlock_init (&lock, &attr);
  93
  94   /* Make standard error the same as standard output.  */
  95   dup2 (1, 2);
  96
  97   /* Make sure we see all message, even those on stdout.  */
  98   setvbuf (stdout, NULL, _IONBF, 0);
  99
 100   for (n = 0; n < THREADS; ++n)
 101     thr[n] = xpthread_create (NULL, tf, (void *) (uintptr_t) n);
 102
 103   struct timespec delay;
 104   delay.tv_sec = 10;
 105   delay.tv_nsec = 0;
 106   nanosleep (&delay, NULL);
 107   atomic_store_relaxed (&done, 1);
 108
 109   /* Wait for all the threads.  */
 110   for (n = 0; n < THREADS; ++n)
 111     xpthread_join (thr[n]);
 112
 113   return 0;
 114 }
 115
 116 #include <support/test-driver.c>