linux-kernel - Re: [RFC PATCH v2 3/8] arm64: Terminate the stack trace at TASK_FRAME and EL0

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Message-ID: <0f36fe36-c435-f12a-661b-7075f899e4fb@linux.microsoft.com>
Date:   Tue, 23 Mar 2021 07:40:49 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Mark Brown <broonie@...nel.org>, jpoimboe@...hat.com,
        jthierry@...hat.com, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 3/8] arm64: Terminate the stack trace at TASK_FRAME
 and EL0_FRAME



On 3/23/21 5:36 AM, Mark Rutland wrote:
> On Thu, Mar 18, 2021 at 03:29:19PM -0500, Madhavan T. Venkataraman wrote:
>>
>>
>> On 3/18/21 1:26 PM, Mark Brown wrote:
>>> On Mon, Mar 15, 2021 at 11:57:55AM -0500, madvenka@...ux.microsoft.com wrote:
>>>
>>>> +	/* Terminal record, nothing to unwind */
>>>> +	if (fp == (unsigned long) regs->stackframe) {
>>>> +		if (regs->frame_type == TASK_FRAME ||
>>>> +		    regs->frame_type == EL0_FRAME)
>>>> +			return -ENOENT;
>>>>  		return -EINVAL;
>>>> +	}
>>>
>>> This is conflating the reliable stacktrace checks (which your series
>>> will later flag up with frame->reliable) with verifying that we found
>>> the bottom of the stack by looking for this terminal stack frame record.
>>> For the purposes of determining if the unwinder got to the bottom of the
>>> stack we don't care what stack type we're looking at, we just care if it
>>> managed to walk to this defined final record.  
>>>
>>> At the minute nothing except reliable stack trace has any intention of
>>> checking the specific return code but it's clearer to be consistent.
>>>
>>
>> So, you are saying that the type check is redundant. OK. I will remove it
>> and just return -ENOENT on reaching the final record.
> 
> Yes please; and please fold that into the same patch that adds the final
> records.
> 

Will do.

Thanks.

Madhavan