watchdog: Improve initialisation error message and documentation

The error message 'NMI watchdog failed to create perf event...'
does not make it clear that this is a fatal error for the
watchdog.  It also currently prints the error value as a
pointer, rather than extracting the error code with PTR_ERR().
Fix that.

Add a note to the description of the 'nowatchdog' kernel
parameter to associate it with this message.

Reported-by: Cesare Leonardi <celeonar@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: 599368@bugs.debian.org
Cc: 608138@bugs.debian.org
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: <stable@kernel.org> # .37.x and later
LKML-Reference: <1294009362.3167.126.camel@localhost>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 3 insertions, 2 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 8b61c9360999..01ece1b9213e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1759,7 +1759,7 @@ and is between 256 and 4096 characters. It is defined in the file
 
         nousb           [USB] Disable the USB subsystem
 
-        nowatchdog      [KNL] Disable the lockup detector.
+        nowatchdog      [KNL] Disable the lockup detector (NMI watchdog).
 
         nowb            [ARM]
 
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 6e3c41a4024c..5b082156cd21 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -364,7 +364,8 @@ static int watchdog_nmi_enable(int cpu)
                 goto out_save;
         }
 
-        printk(KERN_ERR "NMI watchdog failed to create perf event on cpu%i: %p\n", cpu, event);
+        printk(KERN_ERR "NMI watchdog disabled for cpu%i: unable to create perf event: %ld\n",
+               cpu, PTR_ERR(event));
         return PTR_ERR(event);
 
         /* success path */