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[Qemu-devel] [5633] Fix alarm_timer race with select - v3 (Jan Kiszka)
From: |
Anthony Liguori |
Subject: |
[Qemu-devel] [5633] Fix alarm_timer race with select - v3 (Jan Kiszka) |
Date: |
Wed, 05 Nov 2008 20:29:46 +0000 |
Revision: 5633
http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5633
Author: aliguori
Date: 2008-11-05 20:29:45 +0000 (Wed, 05 Nov 2008)
Log Message:
-----------
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 <address@hidden>
Signed-off-by: Anthony Liguori <address@hidden>
Modified Paths:
--------------
trunk/vl.c
Modified: trunk/vl.c
===================================================================
--- trunk/vl.c 2008-11-05 20:24:35 UTC (rev 5632)
+++ trunk/vl.c 2008-11-05 20:29:45 UTC (rev 5633)
@@ -885,6 +885,7 @@
#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 @@
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) {
@@ -1674,7 +1678,21 @@
{
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 @@
/* 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 @@
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);
}
- [Qemu-devel] [5633] Fix alarm_timer race with select - v3 (Jan Kiszka),
Anthony Liguori <=