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authorIzumi Tsutsui <tsutsui@ceres.dti.ne.jp>2013-07-03 17:58:14 +0900
committerAnthony Liguori <aliguori@us.ibm.com>2013-08-05 11:48:00 -0500
commit79761c6681f0d1cc1c027116fcb4382d41ed3ece (patch)
tree9e2ac1f7b46d9a3d02b5cdfe545cfa45edafcc30 /util
parente1d0fb378ae3bb4272124a12e3fe1a02c4745eb1 (diff)
semaphore: fix a hangup problem under load on NetBSD hosts.
Fix following bugs in "fallback implementation of counting semaphores with mutex+condvar" added in c166cb72f1676855816340666c3b618beef4b976: - waiting threads are not restarted properly if more than one threads are waiting unblock signals in qemu_sem_timedwait() - possible missing pthread_cond_signal(3) calls when waiting threads are returned by ETIMEDOUT - fix an uninitialized variable The problem is analyzed by and fix is provided by Noriyuki Soda. Also put additional cleanup suggested by Laszlo Ersek: - make QemuSemaphore.count unsigned (it won't be negative) - check a return value of in pthread_cond_wait() in qemu_sem_wait() Signed-off-by: Izumi Tsutsui <tsutsui@ceres.dti.ne.jp> Reviewed-by: Laszlo Ersek <lersek@redhat.com> Message-id: 1372841894-10634-1-git-send-email-tsutsui@ceres.dti.ne.jp Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'util')
-rw-r--r--util/qemu-thread-posix.c28
1 files changed, 16 insertions, 12 deletions
diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index 4489abf1d8..4de133e7b2 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -170,12 +170,11 @@ void qemu_sem_post(QemuSemaphore *sem)
#if defined(__APPLE__) || defined(__NetBSD__)
pthread_mutex_lock(&sem->lock);
- if (sem->count == INT_MAX) {
+ if (sem->count == UINT_MAX) {
rc = EINVAL;
- } else if (sem->count++ < 0) {
- rc = pthread_cond_signal(&sem->cond);
} else {
- rc = 0;
+ sem->count++;
+ rc = pthread_cond_signal(&sem->cond);
}
pthread_mutex_unlock(&sem->lock);
if (rc != 0) {
@@ -207,19 +206,21 @@ int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
struct timespec ts;
#if defined(__APPLE__) || defined(__NetBSD__)
+ rc = 0;
compute_abs_deadline(&ts, ms);
pthread_mutex_lock(&sem->lock);
- --sem->count;
- while (sem->count < 0) {
+ while (sem->count == 0) {
rc = pthread_cond_timedwait(&sem->cond, &sem->lock, &ts);
if (rc == ETIMEDOUT) {
- ++sem->count;
break;
}
if (rc != 0) {
error_exit(rc, __func__);
}
}
+ if (rc != ETIMEDOUT) {
+ --sem->count;
+ }
pthread_mutex_unlock(&sem->lock);
return (rc == ETIMEDOUT ? -1 : 0);
#else
@@ -249,16 +250,19 @@ int qemu_sem_timedwait(QemuSemaphore *sem, int ms)
void qemu_sem_wait(QemuSemaphore *sem)
{
+ int rc;
+
#if defined(__APPLE__) || defined(__NetBSD__)
pthread_mutex_lock(&sem->lock);
- --sem->count;
- while (sem->count < 0) {
- pthread_cond_wait(&sem->cond, &sem->lock);
+ while (sem->count == 0) {
+ rc = pthread_cond_wait(&sem->cond, &sem->lock);
+ if (rc != 0) {
+ error_exit(rc, __func__);
+ }
}
+ --sem->count;
pthread_mutex_unlock(&sem->lock);
#else
- int rc;
-
do {
rc = sem_wait(&sem->sem);
} while (rc == -1 && errno == EINTR);