Re: [PATCH v5 0/2] arm64: Fix pending single-step debugging issues

From: Luis Machado <luis.machado@arm.com>
To: Daniel Thompson <daniel.thompson@linaro.org>,
	Sumit Garg <sumit.garg@linaro.org>
Cc: will@kernel.org, catalin.marinas@arm.com, liwei391@huawei.com,
	mhiramat@kernel.org, maz@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, mark.rutland@arm.com,
	dianders@chromium.org
Subject: Re: [PATCH v5 0/2] arm64: Fix pending single-step debugging issues
Date: Wed, 25 Jan 2023 09:18:30 +0000	[thread overview]
Message-ID: <d6a92e81-0f67-68ce-744d-149bbcdc06d9@arm.com> (raw)
In-Reply-To: <Y9AdunpawWzWKIXN@aspen.lan>

Hi,

Is this expected to change single-stepping operation in usespace for debuggers (gdb/lldb)? If so, it would be nice to at least
test it a little to make sure it works.

On 1/24/23 18:04, Daniel Thompson wrote:
> On Thu, Jan 12, 2023 at 02:52:49PM +0530, Sumit Garg wrote:
>> Hi Will, Catalin,
>>
>> On Mon, 19 Dec 2022 at 15:55, Sumit Garg <sumit.garg@linaro.org> wrote:
>>>
>>> This patch-set reworks pending fixes from Wei's series [1] to make
>>> single-step debugging via kgdb/kdb on arm64 work as expected. There was
>>> a prior discussion on ML [2] regarding if we should keep the interrupts
>>> enabled during single-stepping. So patch #1 follows suggestion from Will
>>> [3] to not disable interrupts during single stepping but rather skip
>>> single stepping within interrupt handler.
>>>
>>> [1] https://lore.kernel.org/all/20200509214159.19680-1-liwei391@huawei.com/
>>> [2] https://lore.kernel.org/all/CAD=FV=Voyfq3Qz0T3RY+aYWYJ0utdH=P_AweB=13rcV8GDBeyQ@mail.gmail.com/
>>> [3] https://lore.kernel.org/all/20200626095551.GA9312@willie-the-truck/
>>>
>>> Changes in v5:
>>> - Incorporated misc. comments from Mark.
>>>
>>
>> Since patch #1 has already been reviewed/acked by Mark and the
>> complete patchset has been tested by Doug, would it be fine for you to
>> pick up this patchset? It fixes a real single stepping problem for
>> kgdb on arm64.
> 
> Sorry to be quiet for so long.
> 
> Testing this patch set has proven to be a little difficult.
> 
> It certainly fixes the single step tests in the kgdbtest suite.
> That's a good start.
> 
> Unfortunately when testing using qemu/KVM (hosted on NXP
> 2k/Solidrun Honeycomb) the patch set is resulting in instability
> running the built-in self tests (specifically this one:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/misc/kgdbts.c#n74 ). Running this test using the kgdbtest harness
> results in the test failing roughly a third of the time.
> 
> The error reported is that the trap handler tried to unlock a spinlock
> that isn't currently locked. To be honest I suspect this is a generic
> problem that the new feature happens to tickle (this test has
> historically been unreliable on x86 too... and x86 is noteworthy for
> being the only other platform I test using KVM rather than pure qemu).
> Of course the only way to prove that would be to find and fix the
> problem in the trap handler (which probably involves rewriting it) and I
> haven't managed to do that yet.
> 
> In short, I think the debugger is more useful with this patchset than
> without so, although it is caveated by the above, I'd call this:
> 
> Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
> Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
> 
> 
> Daniel.
> 
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