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Fix alarm_timer race with select - v3 (Jan Kiszka) 

Changing the default IO timeout to 5 s (#5578) made a race visible
between the alarm_timer and select() in main_loop_wait(): If the timer
fired before select was able to block, the full select() timeout could
have been applied instead of returning immediately. Since #5578, this
causes heavy problems to the Musicpal board emulation with stalls up to
5 s, but also with some older Linux guest kernels.

The following patch introduces a pipe that is written to by
host_alarm_handler and select()'ed in main_loop_wait(). This avoids
prevents that select() blocks though a timer has fired and waits for
processing.

Signed-off-by: Jan Kiszka <jan.kiszka@web.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5633 c046a42c-6fe2-441c-8c8c-71466251a162
This commit is contained in:
aliguori 2008-11-05 20:29:45 +00:00
parent ffd3925701
commit c96f1a48d2
1 changed files with 26 additions and 2 deletions
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28
vl.c
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@ -885,6 +885,7 @@ static void qemu_rearm_alarm_timer(struct qemu_alarm_timer *t)
#define MIN_TIMER_REARM_US 250
static struct qemu_alarm_timer *alarm_timer;
static int alarm_timer_rfd, alarm_timer_wfd;
#ifdef _WIN32
@ -1304,12 +1305,15 @@ static void host_alarm_handler(int host_signum)
qemu_get_clock(vm_clock))) ||
qemu_timer_expired(active_timers[QEMU_TIMER_REALTIME],
qemu_get_clock(rt_clock))) {
CPUState *env = next_cpu;
static const char byte = 0;
#ifdef _WIN32
struct qemu_alarm_win32 *data = ((struct qemu_alarm_timer*)dwUser)->priv;
SetEvent(data->host_alarm);
#endif
CPUState *env = next_cpu;
write(alarm_timer_wfd, &byte, sizeof(byte));
alarm_timer->flags |= ALARM_FLAG_EXPIRED;
if (env) {
@ -1674,6 +1678,20 @@ static void init_timer_alarm(void)
{
struct qemu_alarm_timer *t = NULL;
int i, err = -1;
int fds[2];
if (pipe(fds) < 0) {
fail:
perror("creating timer pipe");
exit(1);
}
for (i = 0; i < 2; i++) {
int flags = fcntl(fds[i], F_GETFL);
if (flags == -1 || fcntl(fds[i], F_SETFL, flags | O_NONBLOCK))
goto fail;
}
alarm_timer_rfd = fds[0];
alarm_timer_wfd = fds[1];
for (i = 0; alarm_timers[i].name; i++) {
t = &alarm_timers[i];
@ -4426,8 +4444,9 @@ void main_loop_wait(int timeout)
/* poll any events */
/* XXX: separate device handlers from system ones */
nfds = -1;
nfds = alarm_timer_rfd;
FD_ZERO(&rfds);
FD_SET(alarm_timer_rfd, &rfds);
FD_ZERO(&wfds);
FD_ZERO(&xfds);
for(ioh = first_io_handler; ioh != NULL; ioh = ioh->next) {
@ -4501,6 +4520,11 @@ void main_loop_wait(int timeout)
qemu_get_clock(rt_clock));
if (alarm_timer->flags & ALARM_FLAG_EXPIRED) {
char byte;
do {
ret = read(alarm_timer_rfd, &byte, sizeof(byte));
} while (ret != -1 || errno != EAGAIN);
alarm_timer->flags &= ~(ALARM_FLAG_EXPIRED);
qemu_rearm_alarm_timer(alarm_timer);
}