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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Matt Redfearn <matt.redfearn@mips.com>
Cc:     <linux-arch@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        James Hogan <jhogan@kernel.org>, <linux-mips@linux-mips.org>
References: <87604mhrnb.fsf@xmission.com>
        <20180420143811.9994-8-ebiederm@xmission.com>
        <e0a5bde2-7817-3e05-1c8d-c8fa8f6aa5f2@mips.com>
Date:   Wed, 09 May 2018 21:39:20 -0500
In-Reply-To: <e0a5bde2-7817-3e05-1c8d-c8fa8f6aa5f2@mips.com> (Matt Redfearn's
        message of "Wed, 9 May 2018 16:14:40 +0100")
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Subject: Re: [REVIEW][PATCH 08/22] signal/mips: Use force_sig_fault where appropriate
Sender: linux-kernel-owner@vger.kernel.org
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Matt Redfearn <matt.redfearn@mips.com> writes:

> Hi Eric,
>
> On 20/04/18 15:37, Eric W. Biederman wrote:
>> Filling in struct siginfo before calling force_sig_info a tedious and
>> error prone process, where once in a great while the wrong fields
>> are filled out, and siginfo has been inconsistently cleared.
>>
>> Simplify this process by using the helper force_sig_fault.  Which
>> takes as a parameters all of the information it needs, ensures
>> all of the fiddly bits of filling in struct siginfo are done properly
>> and then calls force_sig_info.
>>
>> In short about a 5 line reduction in code for every time force_sig_info
>> is called, which makes the calling function clearer.
>>
>> Cc: Ralf Baechle <ralf@linux-mips.org>
>> Cc: James Hogan <jhogan@kernel.org>
>> Cc: linux-mips@linux-mips.org
>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>> ---
>>   arch/mips/kernel/traps.c | 65 ++++++++++++++----------------------------------
>>   arch/mips/mm/fault.c     | 19 ++++----------
>>   2 files changed, 23 insertions(+), 61 deletions(-)
>>
>> diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
>> index 967e9e4e795e..66ec4b0b484d 100644
>> --- a/arch/mips/kernel/traps.c
>> +++ b/arch/mips/kernel/traps.c
>> @@ -699,17 +699,11 @@ static int simulate_sync(struct pt_regs *regs, unsigned int opcode)
>>   asmlinkage void do_ov(struct pt_regs *regs)
>>   {
>>   	enum ctx_state prev_state;
>> -	siginfo_t info;
>> -
>> -	clear_siginfo(&info);
>> -	info.si_signo = SIGFPE;
>> -	info.si_code = FPE_INTOVF;
>> -	info.si_addr = (void __user *)regs->cp0_epc;
>>     	prev_state = exception_enter();
>>   	die_if_kernel("Integer overflow", regs);
>>   -	force_sig_info(SIGFPE, &info, current);
>> +	force_sig_fault(SIGFPE, FPE_INTOVF, (void __user *)regs->cp0_epc, current);
>>   	exception_exit(prev_state);
>>   }
>>   @@ -722,32 +716,27 @@ asmlinkage void do_ov(struct pt_regs *regs)
>>   void force_fcr31_sig(unsigned long fcr31, void __user *fault_addr,
>>   		     struct task_struct *tsk)
>>   {
>> -	struct siginfo si;
>> -
>> -	clear_siginfo(&si);
>> -	si.si_addr = fault_addr;
>> -	si.si_signo = SIGFPE;
>> +	int si_code;
>
> This is giving build errors in Linux next
> (https://storage.kernelci.org/next/master/next-20180509/mips/defconfig+kselftest/build.log)
>
> si_code would have ended up as 0 before from the clear_siginfo(), but perhaps

And si_code 0 is not a valid si_code to use with a floating point
siginfo layout.

> int si_code = FPE_FLTUNK;
>
> Would make a more sensible default?

FPE_FLTUNK would make a more sensible default.

I seem to remember someone telling me that case can never happen in
practice so I have simply not worried about it.  Perhaps I am
misremembering this.

Eric