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

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Message-Id: <cecc8a28-4e2f-8e03-0b1a-8a9ac60c0c71@linux.vnet.ibm.com>
Date:   Fri, 17 Feb 2017 17:30:23 +0800
From:   Pan Xinhui <xinhui@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        "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



在 2017/2/17 14:05, Michael Ellerman 写道:
> 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.
>
yep, make sense.

>> @@ -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.
>
Although it is not often that kernel got stucked during boot. Yes, the behavior changed anyway. Will fix that in v3.

> cheers
>