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Subject: Re: [PATCH] MIPS: Fix IRQ tracing when call handle_fpe()
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc:     paulburton@kernel.org, chenhc@lemote.com,
        linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
        liulichao@loongson.cn
References: <20200525033123.13114-1-yuanjunqing66@163.com>
 <20200525084234.GA5057@alpha.franken.de>
From:   yuanjunqing <yuanjunqing66@163.com>
Message-ID: <76f2c756-0ae4-83f5-becf-6f1b3319f6fd@163.com>
Date:   Tue, 26 May 2020 15:07:16 +0800
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在 2020/5/25 下午4:42, Thomas Bogendoerfer 写道:
> On Mon, May 25, 2020 at 11:31:23AM +0800, YuanJunQing wrote:
>>  Register "a1" is unsaved in this function,
>>  when CONFIG_TRACE_IRQFLAGS is enabled,
>>  the TRACE_IRQS_OFF macro will call trace_hardirqs_off(),
>>  and this may change register "a1".
>>  The variment of register "a1" may send SIGFPE signal
>>  to task when call do_fpe(),and this may kill the task.
>>
>> Signed-off-by: YuanJunQing <yuanjunqing66@163.com>
>> ---
>>  arch/mips/kernel/genex.S | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
>> index 8236fb291e3f..956a76429773 100644
>> --- a/arch/mips/kernel/genex.S
>> +++ b/arch/mips/kernel/genex.S
>> @@ -480,16 +480,18 @@ NESTED(nmi_handler, PT_SIZE, sp)
>>  	/* gas fails to assemble cfc1 for some archs (octeon).*/ \
>>  	.set	mips1
>>  	SET_HARDFLOAT
>> -	cfc1	a1, fcr31
>> +	cfc1	s0, fcr31
>>  	.set	pop
>>  	CLI
>>  	TRACE_IRQS_OFF
>> +	move    a1,s0
>>  	.endm
> do we realy need to read fcr31 that early ? Wouldn't it work to
> just move the cfc1 below TRACE_IRQS_OFF ?
>
> Thomas.


 yes, it can work when we just move the cfc1 below TRACE_IRQS_OFF,
 and the code is written as follows.

 	CLI
 	TRACE_IRQS_OFF
 	.set	mips1
 	SET_HARDFLOAT
	cfc1	a1, fcr31
 	.set	pop
       .endm