diff options
| author | Sascha Silbe <silbe@linux.vnet.ibm.com> | 2016-01-29 15:51:45 +0100 |
|---|---|---|
| committer | Cornelia Huck <cornelia.huck@de.ibm.com> | 2016-03-01 12:15:28 +0100 |
| commit | fe345a3d5d7ed4bc2965c65542832b1fa785ae9d (patch) | |
| tree | 268159547f42960943a4fcc7affa0433f434ab90 | |
| parent | 8777f6abdbf7017b7aea38dcee2f389f61925ed8 (diff) | |
watchdog/diag288: avoid race condition on expired watchdog
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 <silbe@linux.vnet.ibm.com>
Acked-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
| -rw-r--r-- | hw/watchdog/wdt_diag288.c | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/hw/watchdog/wdt_diag288.c b/hw/watchdog/wdt_diag288.c index 5eb5b94e43..1c3658e4a8 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, |