Re: [PATCH] irqchip/gic-v3-its: Lock its device list during find and create its device

From: Marc Zyngier <marc.zyngier@arm.com>
To: Zheng Xiang <zhengxiang9@huawei.com>
Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de,
	jason@lakedaemon.net, wanghaibin.wang@huawei.com
Subject: Re: [PATCH] irqchip/gic-v3-its: Lock its device list during find and create its device
Date: Thu, 31 Jan 2019 15:12:42 +0000	[thread overview]
Message-ID: <6c44c2d4-d507-e01a-eef5-894ae71209ef@arm.com> (raw)
In-Reply-To: <32354a2a-b1b3-e03b-c486-c17aee1bed8d@huawei.com>

Hi Zeng,

On 31/01/2019 14:47, Zheng Xiang wrote:
> Hi Marc,
> 
> On 2019/1/29 13:42, Zheng Xiang wrote:
>> On 2019/1/28 21:51, Marc Zyngier wrote:
>>> On 28/01/2019 07:13, Zheng Xiang wrote:
>>>> Hi Marc,
>>>>
>>>> Thanks for your review.
>>>>
>>>> On 2019/1/26 19:38, Marc Zyngier wrote:
>>>>> Hi Zheng,
>>>>>
>>>>> On Sat, 26 Jan 2019 06:16:24 +0000,
>>>>> Zheng Xiang <zhengxiang9@huawei.com> wrote:
>>>>>>
>>>>>> Currently each PCI device under a PCI Bridge shares the same device id
>>>>>> and ITS device. Assume there are two PCI devices call its_msi_prepare
>>>>>> concurrently and they are both going to find and create their ITS
>>>>>> device. There is a chance that the later one couldn't find ITS device
>>>>>> before the other one creating the ITS device. It will cause the later
>>>>>> one to create a different ITS device even if they have the same
>>>>>> device_id.
>>>>>
>>>>> Interesting finding. Is this something you've actually seen in practice
>>>>> with two devices being probed in parallel? Or something that you found
>>>>> by inspection?
>>>>
>>>> Yes, I find this problem after analyzing the reason of VM hung. At last, I
>>>> find that the virtio-gpu cannot receive the MSI interrupts due to sharing
>>>> a same event_id as virtio-serial.
>>>>
>>>> See https://lkml.org/lkml/2019/1/10/299 for the bug report.
>>>>
>>>> This problem can be reproducted with high probability by booting a Qemu/KVM
>>>> VM with a virtio-serial controller and a virtio-gpu adding to a PCI Bridge
>>>> and also adding some delay before creating ITS device.
>>>
>>> Fair enough. Do you mind sharing your QEMU command line? It'd be useful
>>> if I could reproduce it here (and would give me a way to check that it
>>> doesn't regress).
>>
> 
> Have you reproduced it with my QEMU command line?
> 
> If so, should I send a V2 patch with your suggestion?

I've queued the following, much more complete patch:

https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=irq/irqchip-next&id=9791ec7df0e7b4d80706ccea8f24b6542f6059e9

Can you check that it works for you? I didn't manage to get the right
timing conditions, but I also had issues getting virtio-gpu running on
my TX2, so one might explain the other.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...