linux-kernel - Re: [PATCH] powerpc/xmon: Fix an unexpected xmon onoff state change

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Date:   Fri, 17 Feb 2017 17:05:48 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Pan Xinhui <xinhui@...ux.vnet.ibm.com>,
        "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, npiggin@...il.com
Subject: Re: [PATCH] powerpc/xmon: Fix an unexpected xmon onoff state change

Pan Xinhui <xinhui@...ux.vnet.ibm.com> writes:
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 9c0e17c..f6e5c3d 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -76,6 +76,7 @@ static int xmon_gate;
>   #endif /* CONFIG_SMP */
>   
>   static unsigned long in_xmon __read_mostly = 0;
> +static int xmon_off = !IS_ENABLED(CONFIG_XMON_DEFAULT);

I think the logic would probably clearer if we invert this to become
xmon_on.

> @@ -3266,16 +3269,16 @@ static int __init setup_xmon_sysrq(void)
>   __initcall(setup_xmon_sysrq);
>   #endif /* CONFIG_MAGIC_SYSRQ */
>   
> -static int __initdata xmon_early, xmon_off;
> +static int __initdata xmon_early;
>   
>   static int __init early_parse_xmon(char *p)
>   {
>   	if (!p || strncmp(p, "early", 5) == 0) {
>   		/* just "xmon" is equivalent to "xmon=early" */
> -		xmon_init(1);
>   		xmon_early = 1;
> +		xmon_off = 0;
>   	} else if (strncmp(p, "on", 2) == 0)
> -		xmon_init(1);
> +		xmon_off = 0;

You've just changed the timing of when xmon gets enabled for the above
two cases, from here which is called very early, to xmon_setup() which
is called much later in boot.

That effectively disables xmon for most of the boot, which we do not
want to do.

cheers