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

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Date:	Mon, 18 Aug 2014 11:05:29 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Don Zickus <dzickus@...hat.com>
Cc:	akpm@...ux-foundation.org, 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>
Subject: Re: [PATCH 3/5] watchdog: fix print-once on enable


* Don Zickus <dzickus@...hat.com> wrote:

> 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;

Looks good except a small detail: two-line blocks need curly 
braces too, even if it's just a single C statement. I've fixed 
this up in the commit.

thanks,

	Ingo

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