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

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Date:   Thu, 16 Feb 2017 08:57:50 -0200
From:   "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        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

On 16/02/2017 03:09, Michael Ellerman wrote:
> Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com> writes:
> 
>> Once xmon is triggered by sysrq-x, it is enabled always afterwards even
>> if it is disabled during boot. This will cause a system reset interrut
>> fail to dump. So keep xmon in its original state after exit.
>>
>> Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
>> ---
>>  arch/powerpc/xmon/xmon.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
>> index 9c0e17c..721212f 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 = 0;
>>  
>>  static unsigned long adrs;
>>  static int size = 1;
>> @@ -3250,6 +3251,8 @@ static void sysrq_handle_xmon(int key)
>>  	/* ensure xmon is enabled */
>>  	xmon_init(1);
>>  	debugger(get_irq_regs());
>> +	if (xmon_off)
>> +		xmon_init(0);
>>  }
> 
> I don't think this is right.
> 
> xmon_off is only true if you boot with xmon=off on the command line.
> 
> So if you boot with CONFIG_XMON_DEFAULT=n, and nothing on the command
> line, then enter xmon via sysrq, then exit, xmon will still be enabled.
> 

Agreed, noticed it after some work in V2 of my patch. I'm addressing it
there, so maybe no harm in keeping this way here..

Thanks,


Guilherme



> cheers
>