Messages in this thread | | | Subject | Re: [PATCH] PCI/IOV: update num_VFs earlier | From | Don Dutile <> | Date | Wed, 9 Oct 2019 10:20:33 -0400 |
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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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