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

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Date:   Thu, 18 Mar 2021 15:29:19 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     mark.rutland@....com, 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 3/18/21 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.

Madhavan