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From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Mark Brown <broonie@kernel.org>
Cc: mark.rutland@arm.com, jpoimboe@redhat.com, ardb@kernel.org,
	jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org,
	jmorris@namei.org, pasha.tatashin@soleen.com,
	linux-arm-kernel@lists.infradead.org,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v4 1/2] arm64: Introduce stack trace reliability checks in the unwinder
Date: Fri, 21 May 2021 12:23:52 -0500	[thread overview]
Message-ID: <a2a32666-c27e-3a0f-06b2-b7a2baa7e0f1@linux.microsoft.com> (raw)
In-Reply-To: <20210521161117.GB5825@sirena.org.uk>



On 5/21/21 11:11 AM, Mark Brown wrote:
> On Sat, May 15, 2021 at 11:00:17PM -0500, madvenka@linux.microsoft.com wrote:
> 
>> Other reliability checks will be added in the future.
> 
> ...
> 
>> +	frame->reliable = true;
>> +
> 
> All these checks are good checks but as you say there's more stuff that
> we need to add (like your patch 2 here) so I'm slightly nervous about
> actually setting the reliable flag here without even a comment.  Equally
> well there's no actual use of this until arch_stack_walk_reliable() gets
> implemented so it's not like it's causing any problems and it gives us
> the structure to start building up the rest of the checks.
> 

OK. So how about changing the field from a flag to an enum that says exactly
what happened with the frame?

enum {
	FRAME_NORMAL = 0,
	FRAME_UNALIGNED,
	FRAME_NOT_ACCESSIBLE,
	FRAME_RECURSION,
	FRAME_GRAPH_ERROR,
	FRAME_INVALID_TEXT_ADDRESS,
	FRAME_UNRELIABLE_FUNCTION,
	FRAME_NUM_STATUS,
} frame_status;

struct stackframe {
	...
	enum frame_status status;
};

unwind_frame()
{
	frame->status = FRAME_NORMAL;

	Then, for each situation, change the status appropriately.
}

Eventually, arch_stack_walk_reliable() could just declare the stack trace
as unreliable if status != FRAME_NORMAL.

Also, the caller can get an exact idea of why the stack trace failed.

Is that acceptable?

> The other thing I guess is the question of if we want to bother flagging
> frames as unrelaible when we return an error; I don't see an issue with
> it and it may turn out to make it easier to do something in the future
> so I'm fine with that
Initially, I thought that there is no need to flag it for errors. But Josh
had a comment that the stack trace is indeed unreliable on errors. Again, the
word unreliable is the one causing the problem.

The above enum-based solution addresses Josh's comment as well.

Let me know if this is good.

Thanks!

Madhavan

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  reply	other threads:[~2021-05-21 17:25 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <68eeda61b3e9579d65698a884b26c8632025e503>
2021-05-16  4:00 ` [RFC PATCH v4 0/2] arm64: Stack " madvenka
2021-05-16  4:00   ` [RFC PATCH v4 1/2] arm64: Introduce stack " madvenka
2021-05-21 16:11     ` Mark Brown
2021-05-21 17:23       ` Madhavan T. Venkataraman [this message]
2021-05-21 17:42         ` Mark Brown
2021-05-21 17:47           ` Madhavan T. Venkataraman
2021-05-21 17:53             ` Mark Brown
2021-05-21 18:48               ` Josh Poimboeuf
2021-05-21 18:59                 ` Madhavan T. Venkataraman
2021-05-21 19:11                   ` Josh Poimboeuf
2021-05-21 19:16                     ` Josh Poimboeuf
2021-05-21 19:41                       ` Madhavan T. Venkataraman
2021-05-21 20:08                         ` Josh Poimboeuf
2021-05-25 21:44               ` Madhavan T. Venkataraman
2021-05-16  4:00   ` [RFC PATCH v4 2/2] arm64: Create a list of SYM_CODE functions, blacklist them " madvenka
2021-05-19  2:06     ` nobuta.keiya
2021-05-19  3:38       ` Madhavan T. Venkataraman
2021-05-19 19:27     ` Mark Brown
2021-05-20  2:00       ` Madhavan T. Venkataraman
2021-05-21 17:18   ` [RFC PATCH v4 0/2] arm64: Stack trace reliability checks " Mark Brown
2021-05-21 17:32     ` Madhavan T. Venkataraman
2021-05-21 17:47       ` Mark Brown
2021-05-21 17:48         ` Madhavan T. Venkataraman

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