From 24fa90499f8b24bcba2960a3316d797f9b80b5e9 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 5 Mar 2015 16:47:14 +0100 Subject: [PATCH] qemu-thread: do not use PTHREAD_MUTEX_ERRORCHECK PTHREAD_MUTEX_ERRORCHECK is completely broken with respect to fork. The way to safely do fork is to bring all threads to a quiescent state by acquiring locks (either in callers---as we do for the iothread mutex---or using pthread_atfork's prepare callbacks) and then release them in the child. The problem is that releasing error-checking locks in the child fails under glibc with EPERM, because the mutex stores a different owner tid than the duplicated thread in the child process. We could make it work for locks acquired via pthread_atfork, by recreating the mutex in the child instead of unlocking it (we know that there are no other threads that could have taken the mutex; but when the lock is acquired in fork's caller that would not be possible. The simplest solution is just to forgo error checking. Signed-off-by: Paolo Bonzini --- util/qemu-thread-posix.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c index 50a29d8f7a..ba67cec62b 100644 --- a/util/qemu-thread-posix.c +++ b/util/qemu-thread-posix.c @@ -51,12 +51,8 @@ static void error_exit(int err, const char *msg) void qemu_mutex_init(QemuMutex *mutex) { int err; - pthread_mutexattr_t mutexattr; - pthread_mutexattr_init(&mutexattr); - pthread_mutexattr_settype(&mutexattr, PTHREAD_MUTEX_ERRORCHECK); - err = pthread_mutex_init(&mutex->lock, &mutexattr); - pthread_mutexattr_destroy(&mutexattr); + err = pthread_mutex_init(&mutex->lock, NULL); if (err) error_exit(err, __func__); } -- 2.11.4.GIT