[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] Re: [PATCH] Fix alarm_timer race with select
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: [PATCH] Fix alarm_timer race with select |
Date: |
Tue, 04 Nov 2008 18:15:31 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
Anthony Liguori wrote:
> Anthony Liguori wrote:
>> Jan Kiszka wrote:
>>
>> Perhaps we should move the alarm timer check rearming out of the main
>> loop and into a qemu_set_fd_handler2() handler?
>
> And now that I think about it, I see no reason why the timer expiration
> checks couldn't be moved to the same handler. I'd have to look more
> closely at how that would interact with icount though.
I cannot yet follow you here. But I my impression is that this will be
an additional change that should come in a separate patch, no?
Find the O_NONBLOCK remark addressed below.
Jan
------------>
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.
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 <address@hidden>
---
vl.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
Index: b/vl.c
===================================================================
--- a/vl.c
+++ b/vl.c
@@ -884,6 +884,7 @@ static void qemu_rearm_alarm_timer(struc
#define MIN_TIMER_REARM_US 250
static struct qemu_alarm_timer *alarm_timer;
+static int alarm_timer_rfd, alarm_timer_wfd;
#ifdef _WIN32
@@ -1303,12 +1304,15 @@ static void host_alarm_handler(int host_
qemu_get_clock(vm_clock))) ||
qemu_timer_expired(active_timers[QEMU_TIMER_REALTIME],
qemu_get_clock(rt_clock))) {
+ CPUState *env = next_cpu;
+ 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) {
@@ -1673,6 +1677,15 @@ static void init_timer_alarm(void)
{
struct qemu_alarm_timer *t = NULL;
int i, err = -1;
+ int fds[2];
+
+ if (pipe(fds) || fcntl(fds[0], F_SETFL, O_NONBLOCK)
+ || fcntl(fds[1], F_SETFL, O_NONBLOCK)) {
+ perror("creating timer pipe");
+ exit(1);
+ }
+ alarm_timer_rfd = fds[0];
+ alarm_timer_wfd = fds[1];
for (i = 0; alarm_timers[i].name; i++) {
t = &alarm_timers[i];
@@ -4427,6 +4440,7 @@ void main_loop_wait(int timeout)
/* XXX: separate device handlers from system ones */
nfds = -1;
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) {
@@ -4500,6 +4514,11 @@ 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);
}
signature.asc
Description: OpenPGP digital signature