watchdog: Fix print-once on enable

This patch avoids printing the message 'enabled on all CPUs,
...' multiple times. For example, the issue can occur in the
following scenario:

1) watchdog_nmi_enable() fails to enable PMU counters and sets
   cpu0_err.

2) 'echo [0|1] > /proc/sys/kernel/nmi_watchdog' is executed to
   disable and re-enable the watchdog mechanism 'on the fly'.

3) If watchdog_nmi_enable() succeeds to enable PMU counters,
   each CPU will print the message because step1 left behind a
   non-zero cpu0_err.

   if (!IS_ERR(event)) {
       if (cpu == 0 || cpu0_err)
           pr_info("enabled on all CPUs, ...")

The patch avoids this by clearing cpu0_err in watchdog_nmi_disable().

Signed-off-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: pbonzini@redhat.com
Link: http://lkml.kernel.org/r/1407768567-171794-4-git-send-email-dzickus@redhat.com
[ Applied small cleanups. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 4c2e11ce542555758979ec97ad28f4eb18fa47de..df5494edf694e9d2561225a1a6df74c8754eeda3 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -506,7 +506,10 @@ static void watchdog_nmi_disable(unsigned int cpu)
                /* should be in cleanup, but blocks oprofile */
                perf_event_release_kernel(event);
        }
-       return;
+       if (cpu == 0) {
+               /* watchdog_nmi_enable() expects this to be zero initially. */
+               cpu0_err = 0;
+       }
 }
 #else
 static int watchdog_nmi_enable(unsigned int cpu) { return 0; }