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Subject: Re: [PATCH] irqchip/gic-v3-its: Lock its device list during find and
 create its device
To:     Marc Zyngier <marc.zyngier@arm.com>
CC:     <linux-kernel@vger.kernel.org>, <tglx@linutronix.de>,
        <jason@lakedaemon.net>, <wanghaibin.wang@huawei.com>
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 <0dc03914-4c8a-4fa1-fb67-f51936c54836@arm.com>
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 <32354a2a-b1b3-e03b-c486-c17aee1bed8d@huawei.com>
 <6c44c2d4-d507-e01a-eef5-894ae71209ef@arm.com>
From:   Zheng Xiang <zhengxiang9@huawei.com>
Message-ID: <f19624cb-b55d-ae30-f479-3079d818887e@huawei.com>
Date:   Fri, 1 Feb 2019 14:41:32 +0800
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On 2019/1/31 23:12, Marc Zyngier wrote:
> 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.
> 

It works for my case, but I worried about the below lines which may
cause memory leak.

@@ -2627,8 +2640,14 @@ static void its_irq_domain_free(struct irq_domain *domain, unsigned int virq,
 		irq_domain_reset_irq_data(data);
 	}

-	/* If all interrupts have been freed, start mopping the floor */
-	if (bitmap_empty(its_dev->event_map.lpi_map,
+	mutex_lock(&its->dev_alloc_lock);
+
+	/*
+	 * If all interrupts have been freed, start mopping the
+	 * floor. This is conditionned on the device not being shared.
+	 */
+	if (!its_dev->shared &&
+	    bitmap_empty(its_dev->event_map.lpi_map,
 			 its_dev->event_map.nr_lpis)) {
 		its_lpi_free(its_dev->event_map.lpi_map,
 			     its_dev->event_map.lpi_base,

It seems that the shared its_dev would never be freed since the value of
its_dev->shared is always *true*.


> Thanks,
> 
> 	M.
> 
-- 

Thanks,
Xiang