Attachment 5671 Details for Bug 12674 – the test program, to be run in gdb as described

the test program, to be run in gdb as described

semtest.c (text/x-csrc), 2.32 KB, created by Don Hatch on 2011-04-14 06:33:17 UTC

(hide)

Description:

Filename:

MIME Type:

Creator: Don Hatch

Created: 2011-04-14 06:33:17 UTC

Size: 2.32 KB

patch

obsolete

>/*
> * semtest.c
> *
> * test program for sem_post/sem_wait race bug,
> * provided by Alberto Bertogli for gentoo bug 93366
> * ( http://bugs.gentoo.org/show_bug.cgi?id=93366 )
> * with later modifications by Don Hatch.
> *
> * Compile and run with something like:
> * gcc -Wall -g semtest.c -lpthread -o semtest
> *
> * Fails extremely infrequently on AMD64;
> * to make it fail reliably requires a debugger
> * with thread-specific breakpoints:
> *     stop thread 2 (waiter) in sem_wait,
> *     stop thread 3 (poster) at the "cmpq $0x0,0x8(%rdi)" in sem_post,
> *     let thread 2 (waiter) resume and stop it in free,
> *     let thread 3 (poster) resume,
> * it fails with "sem_post() in poster: Invalid argument".
> */
>
>#include <stdio.h>
>#include <stdlib.h>
>#include <sched.h>
>#include <pthread.h>
>#include <semaphore.h>
>#include <string.h>
>
>/* we show output every N loops to show we're still alive */
>#define N 500000
>
>/* sem is used to coordinate the waiter and the poster */
>sem_t sem;
>
>/* varsem is the semaphore created and destroyed */
>sem_t *varsem;
>
>
>/* thread 2 */
>void *waiter(void *unused) {
>	unsigned int count = 0;
>	for (;;) {
>		/* create a semaphore */
>		varsem = malloc(sizeof(sem_t));
>		sem_init(varsem, 0, 0);
>
>		/* let the poster know he can post */
>		sem_post(&sem);
>
>		/* wait for poster's post */
>		while (sem_wait(varsem) != 0)
>			perror("sem_wait() in waiter");
>
>		/* destroy the semaphore */
>		if (sem_destroy(varsem) != 0) {
>			perror("destroy failed");
>		}
>
>		/* trash the semaphore memory before freeing it */
>		memset(varsem, '\1', sizeof(sem_t));
>
>		free(varsem);
>
>		count++;
>		if ((count % N) == 0) {
>			printf("waiter\t%u\n", count);
>			fflush(stdout);
>		}
>	}
>}
>
>/* thread 3 */
>void *poster(void *unused) {
>	unsigned int count = 0;
>	for (;;) {
>		/* wait for waiter's notification that we can post varsem */
>		while (sem_wait(&sem) != 0)
>			perror("sem_wait() in poster");
>
>		/* post varsem */
>		if (sem_post(varsem) != 0) {
>			perror("sem_post() in poster");
>			exit(1);
>		}
>
>		count++;
>		if ((count % N) == 0) {
>			printf("poster\t%u\n", count);
>			fflush(stdout);
>		}
>
>	}
>}
>
>
>int main(void) {
>	pthread_t t1, t2;
>
>	sem_init(&sem, 0, 0);
>	printf("sem: %p\n", &sem);
>	fflush(stdout);
>
>	pthread_create(&t1, NULL, &waiter, NULL);
>	pthread_create(&t2, NULL, &poster, NULL);
>
>	pthread_join(t1, NULL);
>	pthread_join(t2, NULL);
>
>	sem_destroy(&sem);
>	return 0;
>}
>

Actions: View

Attachments on bug 12674: 5671 | 6206 | 7196