nptl/tst-rwlock-pwn.c

   1 /* Test rwlock with PREFER_WRITER_NONRECURSIVE_NP (bug 23861).
   2    Copyright (C) 2018-2023 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 <stdio.h>
  20 #include <stdlib.h>
  21 #include <unistd.h>
  22 #include <pthread.h>
  23 #include <support/xthread.h>
  24
  25 /* We choose 10 iterations because this happens to be able to trigger the
  26    stall on contemporary hardware.  */
  27 #define LOOPS 10
  28 /* We need 3 threads to trigger bug 23861.  One thread as a writer, and
  29    two reader threads.  The test verifies that the second-to-last reader
  30    is able to notify the *last* reader that it should be done waiting.
  31    If the second-to-last reader fails to notify the last reader or does
  32    so incorrectly then the last reader may stall indefinitely.  */
  33 #define NTHREADS 3
  34
  35 _Atomic int do_exit;
  36 pthread_rwlockattr_t mylock_attr;
  37 pthread_rwlock_t mylock;
  38
  39 void *
  40 run_loop (void *a)
  41 {
  42   while (!do_exit)
  43     {
  44       if (random () & 1)
  45         {
  46           xpthread_rwlock_wrlock (&mylock);
  47           xpthread_rwlock_unlock (&mylock);
  48         }
  49       else
  50         {
  51           xpthread_rwlock_rdlock (&mylock);
  52           xpthread_rwlock_unlock (&mylock);
  53         }
  54     }
  55   return NULL;
  56 }
  57
  58 int
  59 do_test (void)
  60 {
  61   xpthread_rwlockattr_init (&mylock_attr);
  62   xpthread_rwlockattr_setkind_np (&mylock_attr,
  63                                   PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP);
  64   xpthread_rwlock_init (&mylock, &mylock_attr);
  65
  66   for (int n = 0; n < LOOPS; n++)
  67     {
  68       pthread_t tids[NTHREADS];
  69       do_exit = 0;
  70       for (int i = 0; i < NTHREADS; i++)
  71         tids[i] = xpthread_create (NULL, run_loop, NULL);
  72       /* Let the threads run for some time.  */
  73       sleep (1);
  74       printf ("Exiting...");
  75       fflush (stdout);
  76       do_exit = 1;
  77       for (int i = 0; i < NTHREADS; i++)
  78         xpthread_join (tids[i]);
  79       printf ("done.\n");
  80     }
  81   pthread_rwlock_destroy (&mylock);
  82   pthread_rwlockattr_destroy (&mylock_attr);
  83   return 0;
  84 }
  85
  86 #define TIMEOUT (DEFAULT_TIMEOUT + 3 * LOOPS)
  87 #include <support/test-driver.c>