linux-kernel - [PATCH 3/5] watchdog: fix print-once on enable

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Date:	Mon, 11 Aug 2014 10:49:25 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	akpm@...ux-foundation.org
Cc:	kvm@...r.kernel.org, pbonzini@...hat.com, mingo@...hat.com,
	LKML <linux-kernel@...r.kernel.org>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Andrew Jones <drjones@...hat.com>,
	Don Zickus <dzickus@...hat.com>
Subject: [PATCH 3/5] watchdog: fix print-once on enable

From: Ulrich Obergfell <uobergfe@...hat.com>

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@...hat.com>
Signed-off-by: Andrew Jones <drjones@...hat.com>
Signed-off-by: Don Zickus <dzickus@...hat.com>
---
 kernel/watchdog.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 6d0a891..0838685 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -522,6 +522,9 @@ static void watchdog_nmi_disable(unsigned int cpu)
 		/* should be in cleanup, but blocks oprofile */
 		perf_event_release_kernel(event);
 	}
+	if (cpu == 0)
+		/* watchdog_nmi_enable() expects this to be zero initially. */
+		cpu0_err = 0;
 	return;
 }
 #else
-- 
1.7.1

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