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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>
References: <20190126061624.5260-1-zhengxiang9@huawei.com>
 <86bm438x8n.wl-marc.zyngier@arm.com>
 <27e0b952-111f-f221-bcd7-1a7ceb2840b5@huawei.com>
 <0dc03914-4c8a-4fa1-fb67-f51936c54836@arm.com>
From:   Zheng Xiang <zhengxiang9@huawei.com>
Message-ID: <505e3257-3ef6-69d4-b996-5a1e200e1246@huawei.com>
Date:   Tue, 29 Jan 2019 13:42:53 +0800
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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).

Yes of course, my QEMU command line is below:

qemu-system-aarch64 \
    -name guest=arm64 \
    -machine virt,accel=kvm,usb=off,gic-version=3 \
    -cpu host \
    -bios /usr/share/edk2/aarch64/QEMU_EFI.fd \
    -nodefaults \
    -m 2048 \
    -smp 1 \
    -device ioh3420,port=0x8,chassis=1,id=pci.1,bus=pcie.0,multifunction=on,addr=0x1 \
    -device i82801b11-bridge,id=pci.2,bus=pcie.0,addr=0x2 \
    -device pci-bridge,chassis_nr=3,id=pci.3,bus=pci.2,addr=0x0 \
    -device ioh3420,port=0x9,chassis=4,id=pci.4,bus=pcie.0,addr=0x1.0x1 \
    -device virtio-scsi-pci,id=scsi0,bus=pci.4,addr=0x0 \
    -drive file=/home/zhengxiang/tmp.raw,format=raw,if=none,id=drive-scsi0-0-0-0,cache=none,aio=threads \
    -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1 \
    -drive file=/dev/mapper/VolGroup00-lvol_7,format=raw,if=none,id=drive-virtio-disk0,cache=none,aio=threads \
    -device virtio-blk-pci,scsi=off,bus=pci.1,addr=0x0,drive=drive-virtio-disk0,id=virtio-disk0 \
    -device virtio-gpu-pci,id=video0,bus=pci.3,addr=0x2 \
    -device virtio-serial-pci,id=virtio-serial0,bus=pci.3,addr=0x3 \
    -device usb-ehci,id=usb,bus=pci.3,addr=0x1 \
    -device usb-kbd,id=input1,bus=usb.0,port=2 \
    -monitor telnet:0.0.0.0:22222,server,nowait \
    -vnc 0.0.0.0:8 \
    -msg timestamp=on \
    -serial stdio \

Add *msleep* between *its_find_device* and *its_create_device* to increase the
rate of probability, .

> 
>>
>>>
>>> The whole RID aliasing is such a mess, I wish we never supported
>>> it. Anyway, comments below.
>>>
>>>>
>>>> Signed-off-by: Zheng Xiang <zhengxiang9@huawei.com>
>>>> ---
>>>>  drivers/irqchip/irq-gic-v3-its.c | 52 +++++++++++++++-------------------------
>>>>  1 file changed, 19 insertions(+), 33 deletions(-)
>>>>
>>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>>>> index db20e99..397edc8 100644
>>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>>> @@ -2205,25 +2205,6 @@ static void its_cpu_init_collections(void)
>>>>  	raw_spin_unlock(&its_lock);
>>>>  }
>>>>  
>>>> -static struct its_device *its_find_device(struct its_node *its, u32 dev_id)
>>>> -{
>>>> -	struct its_device *its_dev = NULL, *tmp;
>>>> -	unsigned long flags;
>>>> -
>>>> -	raw_spin_lock_irqsave(&its->lock, flags);
>>>> -
>>>> -	list_for_each_entry(tmp, &its->its_device_list, entry) {
>>>> -		if (tmp->device_id == dev_id) {
>>>> -			its_dev = tmp;
>>>> -			break;
>>>> -		}
>>>> -	}
>>>> -
>>>> -	raw_spin_unlock_irqrestore(&its->lock, flags);
>>>> -
>>>> -	return its_dev;
>>>> -}
>>>> -
>>>>  static struct its_baser *its_get_baser(struct its_node *its, u32 type)
>>>>  {
>>>>  	int i;
>>>> @@ -2321,7 +2302,7 @@ static bool its_alloc_vpe_table(u32 vpe_id)
>>>>  static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>>>>  					    int nvecs, bool alloc_lpis)
>>>>  {
>>>> -	struct its_device *dev;
>>>> +	struct its_device *dev = NULL, *tmp;
>>>>  	unsigned long *lpi_map = NULL;
>>>>  	unsigned long flags;
>>>>  	u16 *col_map = NULL;
>>>> @@ -2331,6 +2312,24 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id,
>>>>  	int nr_ites;
>>>>  	int sz;
>>>>  
>>>> +	raw_spin_lock_irqsave(&its->lock, flags);
>>>> +	list_for_each_entry(tmp, &its->its_device_list, entry) {
>>>> +		if (tmp->device_id == dev_id) {
>>>> +			dev = tmp;
>>>> +			break;
>>>> +		}
>>>> +	}
>>>> +	if (dev) {
>>>> +		/*
>>>> +		 * We already have seen this ID, probably through
>>>> +		 * another alias (PCI bridge of some sort). No need to
>>>> +		 * create the device.
>>>> +		 */
>>>> +		pr_debug("Reusing ITT for devID %x\n", dev_id);
>>>> +		raw_spin_unlock_irqrestore(&its->lock, flags);
>>>> +		return dev;
>>>> +	}
>>>> +
>>>>  	if (!its_alloc_device_table(its, dev_id))
>>>
>>> You're now performing all sort of allocations in an atomic context,
>>> which is pretty horrible (and the kernel will shout at you for doing
>>> so).
>>>
>>> We could probably keep the current logic and wrap it around a mutex
>>> instead, which would give us the appropriate guarantees WRT allocations.
>>> Something along those lines (untested):>
>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>>> index db20e992a40f..99feb62e63ba 100644
>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>> @@ -97,9 +97,14 @@ struct its_device;
>>>   * The ITS structure - contains most of the infrastructure, with the
>>>   * top-level MSI domain, the command queue, the collections, and the
>>>   * list of devices writing to it.
>>> + *
>>> + * alloc_lock has to be taken for any allocation that can happen at
>>> + * run time, while the spinlock must be taken to parse data structures
>>> + * such as the device list.
>>>   */
>>>  struct its_node {
>>>  	raw_spinlock_t		lock;
>>> +	struct mutex		alloc_lock;
>>>  	struct list_head	entry;
>>>  	void __iomem		*base;
>>>  	phys_addr_t		phys_base;
>>> @@ -2421,6 +2426,7 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
>>>  	struct its_device *its_dev;
>>>  	struct msi_domain_info *msi_info;
>>>  	u32 dev_id;
>>> +	int err = 0;
>>>  
>>>  	/*
>>>  	 * We ignore "dev" entierely, and rely on the dev_id that has
>>> @@ -2443,6 +2449,7 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
>>>  		return -EINVAL;
>>>  	}
>>>  
>>> +	mutex_lock(&its->alloc_lock);
>>>  	its_dev = its_find_device(its, dev_id);
>>>  	if (its_dev) {
>>>  		/*
>>> @@ -2455,11 +2462,14 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
>>>  	}
>>>  
>>>  	its_dev = its_create_device(its, dev_id, nvec, true);
>>> -	if (!its_dev)
>>> -		return -ENOMEM;
>>> +	if (!its_dev) {
>>> +		err = -ENOMEM;
>>> +		goto out;
>>> +	}
>>>  
>>>  	pr_debug("ITT %d entries, %d bits\n", nvec, ilog2(nvec));
>>>  out:
>>> +	mutex_unlock(&its->alloc_lock);
>>>  	info->scratchpad[0].ptr = its_dev;>>>  	return 0;
>>
>> Should it return *err* here?
> 
> Absolutely. Does it fix the problem for you?

Yes, VM doesn't get hung anymore after thousands of times of boot/reboot.

> 
> Thanks,
> 
> 	M.
> 
-- 

Thanks,
Xiang