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SubjectRe: [PATCH] PCI/IOV: update num_VFs earlier
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On 10/09/2019 08:31 AM, Bjorn Helgaas wrote:
> On Tue, Oct 08, 2019 at 06:06:46PM -0400, Don Dutile wrote:
>> On 10/08/2019 05:38 PM, Bjorn Helgaas wrote:
>>> On Thu, Oct 03, 2019 at 05:10:07PM -0500, Bjorn Helgaas wrote:
>>>> On Thu, Oct 03, 2019 at 11:04:45AM +0200, CREGUT Pierre IMT/OLN wrote:
>>>>> ...
>>>
>>>>> NIC drivers send netlink events when their state change, but it is
>>>>> the core that changes the value of num_vfs. So I would think it is
>>>>> the core responsibility to make sure the exposed value makes sense
>>>>> and it would be better to ignore the details of the driver
>>>>> implementation.
>>>>
>>>> Yes, I think you're right. And I like your previous suggestion of
>>>> just locking the device in the reader. I'm not enough of a sysfs
>>>> expert to know if there's a good reason to avoid a lock there. Does
>>>> the following look reasonable to you?
>>>
>>> I applied the patch below to pci/virtualization for v5.5, thanks for
>> I hope not... see below
>>
>>> your great patience!
>>>
>>>> commit 0940fc95da45
>>>> Author: Pierre Crégut <pierre.cregut@orange.com>
>>>> Date: Wed Sep 11 09:27:36 2019 +0200
>>>>
>>>> PCI/IOV: Serialize sysfs sriov_numvfs reads vs writes
>>>> When sriov_numvfs is being updated, drivers may notify about new devices
>>>> before they are reflected in sriov->num_VFs, so concurrent sysfs reads
>>>> previously returned stale values.
>>>> Serialize the sysfs read vs the write so the read returns the correct
>>>> num_VFs value.
>>>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=202991
>>>> Link: https://lore.kernel.org/r/20190911072736.32091-1-pierre.cregut@orange.com
>>>> Signed-off-by: Pierre Crégut <pierre.cregut@orange.com>
>>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>>>
>>>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>>> index b3f972e8cfed..e77562aabbae 100644
>>>> --- a/drivers/pci/iov.c
>>>> +++ b/drivers/pci/iov.c
>>>> @@ -254,8 +254,14 @@ static ssize_t sriov_numvfs_show(struct device *dev,
>>>> char *buf)
>>>> {
>>>> struct pci_dev *pdev = to_pci_dev(dev);
>>>> + u16 num_vfs;
>>>> +
>>>> + /* Serialize vs sriov_numvfs_store() so readers see valid num_VFs */
>>>> + device_lock(&pdev->dev);
>> ^^^^^ lock
>>>> + num_vfs = pdev->sriov->num_VFs;
>>>> + device_lock(&pdev->dev);
>> ^^^^ and lock again!
>
> Oops, sorry, my fault. Fixed.
>
Thanks.
--dd

>>>> - return sprintf(buf, "%u\n", pdev->sriov->num_VFs);
>>>> + return sprintf(buf, "%u\n", num_vfs);
>>>> }
>>>> /*
>>

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