From fe345a3d5d7ed4bc2965c65542832b1fa785ae9d Mon Sep 17 00:00:00 2001 From: Sascha Silbe Date: Fri, 29 Jan 2016 15:51:45 +0100 Subject: watchdog/diag288: avoid race condition on expired watchdog MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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(-) (limited to 'hw/watchdog') 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, -- cgit v1.1