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 your great patience! > commit 0940fc95da45 > Author: Pierre Crégut <pierre.cregut@xxxxxxxxxx> > 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@xxxxxxxxxx > Signed-off-by: Pierre Crégut <pierre.cregut@xxxxxxxxxx> > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > 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); > + num_vfs = pdev->sriov->num_VFs; > + device_lock(&pdev->dev); > > - return sprintf(buf, "%u\n", pdev->sriov->num_VFs); > + return sprintf(buf, "%u\n", num_vfs); > } > > /*
