From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: broonie@kernel.org, mark.rutland@arm.com, 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 v3 1/4] arm64: Introduce stack trace reliability checks in the unwinder
Date: Tue, 4 May 2021 19:21:37 -0500 [thread overview]
Message-ID: <2fc9a77a-ddf5-812a-0681-ece94b433d71@linux.microsoft.com> (raw)
In-Reply-To: <20210505000728.yxg3xbwa3emcu2wi@treble>
On 5/4/21 7:07 PM, Josh Poimboeuf wrote:
> On Tue, May 04, 2021 at 06:13:39PM -0500, Madhavan T. Venkataraman wrote:
>>
>>
>> On 5/4/21 4:52 PM, Josh Poimboeuf wrote:
>>> On Mon, May 03, 2021 at 12:36:12PM -0500, madvenka@linux.microsoft.com wrote:
>>>> @@ -44,6 +44,8 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
>>>> unsigned long fp = frame->fp;
>>>> struct stack_info info;
>>>>
>>>> + frame->reliable = true;
>>>> +
>>>
>>> Why set 'reliable' to true on every invocation of unwind_frame()?
>>> Shouldn't it be remembered across frames?
>>>
>>
>> This is mainly for debug purposes in case a caller wants to print the whole stack and also
>> print which functions are unreliable. For livepatch, it does not make any difference. It will
>> quit as soon as it encounters an unreliable frame.
>
> Hm, ok. So 'frame->reliable' refers to the current frame, not the
> entire stack.
>
Yes.
>>> Also, it looks like there are several error scenarios where it returns
>>> -EINVAL but doesn't set 'reliable' to false.
>>>
>>
>> I wanted to make a distinction between an error situation (like stack corruption where unwinding
>> has to stop) and an unreliable situation (where unwinding can still proceed). E.g., when a
>> stack trace is taken for informational purposes or debug purposes, the unwinding will try to
>> proceed until either the stack trace ends or an error happens.
>
> Ok, but I don't understand how that relates to my comment.
>
> Why wouldn't a stack corruption like !on_accessible_stack() set
> 'frame->reliable' to false?
>
I do see your point. If an error has been hit, then the stack trace is essentially unreliable
regardless of anything else. So, I accept your comment. I will mark the stack trace as unreliable
if any kind of error is encountered.
Thanks!
Madhavan
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next prev parent reply other threads:[~2021-05-05 0:23 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <65cf4dfbc439b010b50a0c46ec500432acde86d6>
2021-05-03 17:36 ` [RFC PATCH v3 0/4] arm64: Stack trace reliability checks in the unwinder madvenka
2021-05-03 17:36 ` [RFC PATCH v3 1/4] arm64: Introduce stack " madvenka
2021-05-04 15:50 ` Mark Brown
2021-05-04 19:14 ` Madhavan T. Venkataraman
2021-05-04 21:52 ` Josh Poimboeuf
2021-05-04 23:13 ` Madhavan T. Venkataraman
2021-05-05 0:07 ` Josh Poimboeuf
2021-05-05 0:21 ` Madhavan T. Venkataraman [this message]
2021-05-03 17:36 ` [RFC PATCH v3 2/4] arm64: Check the return PC against unreliable code sections madvenka
2021-05-04 16:05 ` Mark Brown
2021-05-04 19:03 ` Madhavan T. Venkataraman
2021-05-04 19:32 ` Madhavan T. Venkataraman
2021-05-05 16:46 ` Mark Brown
2021-05-05 18:48 ` Madhavan T. Venkataraman
2021-05-05 18:50 ` Madhavan T. Venkataraman
2021-05-06 13:45 ` Mark Brown
2021-05-06 15:21 ` Madhavan T. Venkataraman
2021-05-05 16:34 ` Mark Brown
2021-05-05 17:51 ` Madhavan T. Venkataraman
2021-05-05 19:30 ` Ard Biesheuvel
2021-05-05 20:00 ` Madhavan T. Venkataraman
2021-05-03 17:36 ` [RFC PATCH v3 3/4] arm64: Handle miscellaneous functions in .text and .init.text madvenka
2021-05-06 14:12 ` Mark Brown
2021-05-06 15:30 ` Madhavan T. Venkataraman
2021-05-06 15:32 ` Madhavan T. Venkataraman
2021-05-06 15:44 ` Mark Brown
2021-05-06 15:56 ` Madhavan T. Venkataraman
2021-05-06 15:37 ` Mark Brown
2021-05-06 15:57 ` Madhavan T. Venkataraman
2021-05-03 17:36 ` [RFC PATCH v3 4/4] arm64: Handle funtion graph tracer better in the unwinder madvenka
2021-05-06 14:43 ` Mark Brown
2021-05-06 15:20 ` Madhavan T. Venkataraman
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