From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Kxn6k-0003qQ-8G for qemu-devel@nongnu.org; Wed, 05 Nov 2008 13:27:58 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Kxn6i-0003pp-Ro for qemu-devel@nongnu.org; Wed, 05 Nov 2008 13:27:58 -0500 Received: from [199.232.76.173] (port=52798 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Kxn6i-0003pk-K6 for qemu-devel@nongnu.org; Wed, 05 Nov 2008 13:27:56 -0500 Received: from lizzard.sbs.de ([194.138.37.39]:15317) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1Kxn6i-0001po-1V for qemu-devel@nongnu.org; Wed, 05 Nov 2008 13:27:56 -0500 Received: from mail2.sbs.de (localhost [127.0.0.1]) by lizzard.sbs.de (8.12.11.20060308/8.12.11) with ESMTP id mA5IRrLQ010734 for ; Wed, 5 Nov 2008 19:27:54 +0100 Received: from [139.25.109.167] (mchn012c.mchp.siemens.de [139.25.109.167] (may be forged)) by mail2.sbs.de (8.12.11.20060308/8.12.11) with ESMTP id mA5IRreD011771 for ; Wed, 5 Nov 2008 19:27:53 +0100 Message-ID: <4911E5AA.1000408@siemens.com> Date: Wed, 05 Nov 2008 19:27:54 +0100 From: Jan Kiszka MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] [PATCH] Fix alarm_timer race with select - v3 Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org [ changes: correct nfds initialization, more robust O_NONBLOCK setup ] 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 --- vl.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) Index: b/vl.c =================================================================== --- a/vl.c +++ b/vl.c @@ -885,6 +885,7 @@ 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 @@ -1304,12 +1305,15 @@ 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) { @@ -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); } -- Siemens AG, Corporate Technology, CT SE 2 ES-OS Corporate Competence Center Embedded Linux