xen/watchdog: Identify which domain watchdog fired

When a watchdog fires, the domain is crashed and can't dump any state.

Xen allows a domain to have two separate watchdogs.  Therefore, for a
domain running multiple watchdogs (e.g. one based around network, one
for disk), it is important for diagnostics to know which watchdog
fired.

As the printk() is in a timer callback, this is a bit awkward to
arrange, but there are 12 spare bits in the bottom of the domain
pointer owing to its alignment.

Reuse these bits to encode the watchdog id too, so the one which fired
is identified when the domain is crashed.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>

diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
index d6296d99fdb922ff62ecaab6b64d956dce0d7155..9043414290a8efbe8446c9eb88703b93513324b5 100644 (file)
--- a/xen/common/sched/core.c
+++ b/xen/common/sched/core.c
@@ -1534,12 +1534,19 @@ long vcpu_yield(void)
 
 static void cf_check domain_watchdog_timeout(void *data)
 {
-    struct domain *d = data;
+    /*
+     * The data parameter encodes the watchdog id in the low bits of
+     * the domain pointer.
+     */
+    struct domain *d = _p((unsigned long)data & PAGE_MASK);
+    unsigned int id = (unsigned long)data & ~PAGE_MASK;
+
+    BUILD_BUG_ON(alignof(*d) < PAGE_SIZE);
 
     if ( d->is_shutting_down || d->is_dying )
         return;
 
-    printk("Watchdog timer fired for domain %u\n", d->domain_id);
+    printk("Watchdog timer %u fired for %pd\n", id, d);
     domain_shutdown(d, SHUTDOWN_watchdog);
 }
 
@@ -1593,7 +1600,17 @@ void watchdog_domain_init(struct domain *d)
     d->watchdog_inuse_map = 0;
 
     for ( i = 0; i < NR_DOMAIN_WATCHDOG_TIMERS; i++ )
-        init_timer(&d->watchdog_timer[i], domain_watchdog_timeout, d, 0);
+    {
+        void *data = d;
+
+        BUILD_BUG_ON(NR_DOMAIN_WATCHDOG_TIMERS > alignof(*d));
+
+        /*
+         * For the timer callback parameter, encode the watchdog id in
+         * the low bits of the domain pointer.
+         */
+        init_timer(&d->watchdog_timer[i], domain_watchdog_timeout, data + i, 0);
+    }
 }
 
 void watchdog_domain_destroy(struct domain *d)