[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Bug 1887306] Re: qemu-user deadlocks when forked in a multithreaded pro
From: |
Thomas Huth |
Subject: |
[Bug 1887306] Re: qemu-user deadlocks when forked in a multithreaded process |
Date: |
Wed, 26 May 2021 14:36:23 -0000 |
This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:
https://gitlab.com/qemu-project/qemu/-/issues/358
** Changed in: qemu
Status: New => Expired
** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #358
https://gitlab.com/qemu-project/qemu/-/issues/358
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1887306
Title:
qemu-user deadlocks when forked in a multithreaded process
Status in QEMU:
Expired
Bug description:
The following program (also attached) deadlocks when run under QEMU
user on Linux.
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#define NUM_THREADS 100
#define NUM_FORKS 10
pthread_barrier_t barrier;
void *t(void *arg) {
for (int i = 0; i < NUM_FORKS; i++) {
pid_t pid = fork();
if (pid < 0)
abort();
if (!pid)
_exit(0);
if (waitpid(pid, NULL, 0) < 0)
abort();
}
//pthread_barrier_wait(&barrier);
return NULL;
}
int main(void) {
pthread_barrier_init(&barrier, NULL, NUM_THREADS);
pthread_t ts[NUM_THREADS];
for (size_t i = 0; i < NUM_THREADS; i++) {
if (pthread_create(&ts[i], NULL, t, NULL))
abort();
}
for (size_t i = 0; i < NUM_THREADS; i++) {
pthread_join(ts[i], NULL);
}
printf("Done: %d\n", getpid());
return 0;
}
To reproduce:
$ gcc test.c -pthread
$ while qemu-x86_64 ./a.out; do :; done
(Be careful, Ctrl-C/SIGINT doesn't kill the deadlocked child).
Larger values of NUM_THREADS/NUM_FORKS lead to more often deadlocks.
With the values above it often deadlocks on the first try on my
machine. When it deadlocks, there is a child qemu process with two
threads which is waited upon by one of the worker threads of the
parent.
I tried to avoid the deadlock by serializing fork() with a mutex, but
it didn't help. However, ensuring that no thread exits until all forks
are done (by adding a barrier to t()) does seem to help, at least, the
program above could run for a half an hour until I terminated it.
Tested on QEMU 5.0.0, 4.2.0 and 2.11.1, with x86_64 and AArch64 linux-
user targets.
To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1887306/+subscriptions