From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35074) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aYB0B-0000ke-9C for qemu-devel@nongnu.org; Tue, 23 Feb 2016 06:19:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aYB07-0000GJ-8c for qemu-devel@nongnu.org; Tue, 23 Feb 2016 06:19:35 -0500 Received: from e06smtp15.uk.ibm.com ([195.75.94.111]:48732) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aYB07-0000G3-0L for qemu-devel@nongnu.org; Tue, 23 Feb 2016 06:19:31 -0500 Received: from localhost by e06smtp15.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 23 Feb 2016 11:19:29 -0000 Received: from b06cxnps4074.portsmouth.uk.ibm.com (d06relay11.portsmouth.uk.ibm.com [9.149.109.196]) by d06dlp03.portsmouth.uk.ibm.com (Postfix) with ESMTP id 492301B0804B for ; Tue, 23 Feb 2016 11:19:34 +0000 (GMT) Received: from d06av09.portsmouth.uk.ibm.com (d06av09.portsmouth.uk.ibm.com [9.149.37.250]) by b06cxnps4074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u1NBJFlY131398 for ; Tue, 23 Feb 2016 11:19:15 GMT Received: from d06av09.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av09.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u1NBJEG1008480 for ; Tue, 23 Feb 2016 04:19:14 -0700 From: Cornelia Huck Date: Tue, 23 Feb 2016 12:19:05 +0100 Message-Id: <1456226350-3367-6-git-send-email-cornelia.huck@de.ibm.com> In-Reply-To: <1456226350-3367-1-git-send-email-cornelia.huck@de.ibm.com> References: <1456226350-3367-1-git-send-email-cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH 05/10] watchdog/diag288: avoid race condition on expired watchdog List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Cornelia Huck , borntraeger@de.ibm.com, jfrei@linux.vnet.ibm.com, agraf@suse.de, Sascha Silbe From: Sascha Silbe When configured to inject an NMI, watchdog_perform_action() may cause the BQL to be temporarily relinquished (inject_nmi() → ... → s390_nmi() → s390_cpu_restart() → run_on_cpu()). When the guest issues diag 288 again in response to the NMI, the diag 288 operation will race against wdt_diag288_reset(). Depending on scheduler behaviour, wdt_diag288_reset() may be run after the guest issued a diag 288 Init. As a result, we will cancel the timer the guest just set up. The effect observed by the guest is that a second expiry does not trigger the watchdog action and diag 288 Change operations fail. Fix this by resetting the timer _before_ invoking the action. Signed-off-by: Sascha Silbe Acked-by: David Hildenbrand Signed-off-by: Cornelia Huck --- hw/watchdog/wdt_diag288.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/hw/watchdog/wdt_diag288.c b/hw/watchdog/wdt_diag288.c index 5eb5b94..1c3658e 100644 --- a/hw/watchdog/wdt_diag288.c +++ b/hw/watchdog/wdt_diag288.c @@ -51,15 +51,19 @@ static void diag288_reset(void *opaque) static void diag288_timer_expired(void *dev) { qemu_log_mask(CPU_LOG_RESET, "Watchdog timer expired.\n"); - watchdog_perform_action(); - /* Reset the watchdog only if the guest was notified about expiry. */ + /* Reset the watchdog only if the guest gets notified about + * expiry. watchdog_perform_action() may temporarily relinquish + * the BQL; reset before triggering the action to avoid races with + * diag288 instructions. */ switch (get_watchdog_action()) { case WDT_DEBUG: case WDT_NONE: case WDT_PAUSE: - return; + break; + default: + wdt_diag288_reset(dev); } - wdt_diag288_reset(dev); + watchdog_perform_action(); } static int wdt_diag288_handle_timer(DIAG288State *diag288, -- 2.7.1