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


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