mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-08 14:20:07 +00:00
109 lines
3.4 KiB
C
109 lines
3.4 KiB
C
/* Bug 23844: Test for pthread_rwlock_trywrlock stalls.
|
|
Copyright (C) 2019-2024 Free Software Foundation, Inc.
|
|
This file is part of the GNU C Library.
|
|
|
|
The GNU C Library is free software; you can redistribute it and/or
|
|
modify it under the terms of the GNU Lesser General Public
|
|
License as published by the Free Software Foundation; either
|
|
version 2.1 of the License, or (at your option) any later version.
|
|
|
|
The GNU C Library is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
Lesser General Public License for more details.
|
|
|
|
You should have received a copy of the GNU Lesser General Public
|
|
License along with the GNU C Library; if not, see
|
|
<https://www.gnu.org/licenses/>. */
|
|
|
|
/* For a full analysis see comments in tst-rwlock-tryrdlock-stall.c.
|
|
|
|
Summary for the pthread_rwlock_trywrlock() stall:
|
|
|
|
The stall is caused by pthread_rwlock_trywrlock setting
|
|
__wrphase_futex futex to 1 and losing the
|
|
PTHREAD_RWLOCK_FUTEX_USED bit.
|
|
|
|
The fix for bug 23844 ensures that waiters on __wrphase_futex are
|
|
correctly woken. Before the fix the test stalls as readers can
|
|
wait forever on __wrphase_futex. */
|
|
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <unistd.h>
|
|
#include <pthread.h>
|
|
#include <support/xthread.h>
|
|
#include <errno.h>
|
|
|
|
/* We need only one lock to reproduce the issue. We will need multiple
|
|
threads to get the exact case where we have a read, try, and unlock
|
|
all interleaving to produce the case where the readers are waiting
|
|
and the try clears the PTHREAD_RWLOCK_FUTEX_USED bit and a
|
|
subsequent unlock fails to wake them. */
|
|
pthread_rwlock_t onelock;
|
|
|
|
/* The number of threads is arbitrary but empirically chosen to have
|
|
enough threads that we see the condition where waiting readers are
|
|
not woken by a successful unlock. */
|
|
#define NTHREADS 32
|
|
|
|
_Atomic int do_exit;
|
|
|
|
void *
|
|
run_loop (void *arg)
|
|
{
|
|
int i = 0, ret;
|
|
while (!do_exit)
|
|
{
|
|
/* Arbitrarily choose if we are the writer or reader. Choose a
|
|
high enough ratio of readers to writers to make it likely
|
|
that readers block (and eventually are susceptable to
|
|
stalling).
|
|
|
|
If we are a writer, take the write lock, and then unlock.
|
|
If we are a reader, try the lock, then lock, then unlock. */
|
|
if ((i % 8) != 0)
|
|
{
|
|
if ((ret = pthread_rwlock_trywrlock (&onelock)) != 0)
|
|
{
|
|
if (ret == EBUSY)
|
|
xpthread_rwlock_wrlock (&onelock);
|
|
else
|
|
exit (EXIT_FAILURE);
|
|
}
|
|
}
|
|
else
|
|
xpthread_rwlock_rdlock (&onelock);
|
|
/* Thread does some work and then unlocks. */
|
|
xpthread_rwlock_unlock (&onelock);
|
|
i++;
|
|
}
|
|
return NULL;
|
|
}
|
|
|
|
int
|
|
do_test (void)
|
|
{
|
|
int i;
|
|
pthread_t tids[NTHREADS];
|
|
xpthread_rwlock_init (&onelock, NULL);
|
|
for (i = 0; i < NTHREADS; i++)
|
|
tids[i] = xpthread_create (NULL, run_loop, NULL);
|
|
/* Run for some amount of time. The pthread_rwlock_tryrwlock stall
|
|
is very easy to trigger and happens in seconds under the test
|
|
conditions. */
|
|
sleep (10);
|
|
/* Then exit. */
|
|
printf ("INFO: Exiting...\n");
|
|
do_exit = 1;
|
|
/* If any readers stalled then we will timeout waiting for them. */
|
|
for (i = 0; i < NTHREADS; i++)
|
|
xpthread_join (tids[i]);
|
|
printf ("INFO: Done.\n");
|
|
xpthread_rwlock_destroy (&onelock);
|
|
printf ("PASS: No pthread_rwlock_tryrwlock stalls detected.\n");
|
|
return 0;
|
|
}
|
|
|
|
#include <support/test-driver.c>
|