From c96f1a48d229a6080fecce4ea20bc64cabe79e32 Mon Sep 17 00:00:00 2001 From: aliguori Date: Wed, 5 Nov 2008 20:29:45 +0000 Subject: [PATCH] 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 Signed-off-by: Anthony Liguori git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5633 c046a42c-6fe2-441c-8c8c-71466251a162 --- vl.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/vl.c b/vl.c index ea9e6529e9..05206c1b4c 100644 --- a/vl.c +++ b/vl.c @@ -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); } -- GitLab