Messages in this thread | | | Subject | Re: [Linuxarm] [PATCH 1/2] hisi_acc_vfio_pci: Add debugfs to migration driver | From | liulongfang <> | Date | Wed, 19 Oct 2022 15:17:44 +0800 |
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On 2022/10/18 20:01, Jason Gunthorpe Wrote: > On Tue, Oct 18, 2022 at 03:06:43PM +0800, liulongfang wrote: >> On 2022/10/17 20:11, Jason Gunthorpe Wrote: >>> On Mon, Oct 17, 2022 at 05:20:34PM +0800, liulongfang wrote: >>>> On 2022/10/14 17:20, John Garry wrote: >>>>> On 14/10/2022 03:57, Longfang Liu wrote: >>>>>> +static void hisi_acc_vf_debugfs_init(struct hisi_acc_vf_core_device *hisi_acc_vdev) >>>>>> +{ >>>>>> + struct pci_dev *vf_pdev = hisi_acc_vdev->vf_dev; >>>>>> + struct device *dev = &vf_pdev->dev; >>>>>> + int ret; >>>>>> + >>>>>> + if (!atomic_read(&hisi_acc_root_ref)) >>>>>> + hisi_acc_debugfs_root = debugfs_create_dir("hisi_vfio_acc", NULL); >>>>>> + atomic_inc(&hisi_acc_root_ref); >>>>>> + >>>>> >>>>> This looks totally racy, such that I wonder why even bother using an atomic for hisi_acc_root_ref. >>>> >>>> >>>> When enabling VF, it is possible for multiple VMs to enable VF at the same time. The atomic variable >>>> is used to ensure that only one "hisi_vfio_acc" is created. When other VFs are enabled, >>>> it will not be created again, but will be used directly. >>> >>> It is still completely racy. Use a lock >>>
Um! I understand your previous solution. Since we did not put module_init() in the driver, to avoid competition, we first need to modify the module_init() interface of the driver, then put debugfs_create_dir() into module_init(), and finally put debugfs_create_file() into probe().
I will implement this way in the next version.
>> >> Do you have any suggested solutions? > > If you want to keep it like this, use a lock around the creation. > > Jason > . > Thanks, Longfang
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