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

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Date:   Tue, 23 Mar 2021 10:36:44 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.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 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.

Thanks,
Mark.