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@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); > ^^^^^ lock > > > + num_vfs = pdev->sriov->num_VFs; > > > + device_lock(&pdev->dev); > ^^^^ and lock again! Oops, sorry, my fault. Fixed. > > > - return sprintf(buf, "%u\n", pdev->sriov->num_VFs); > > > + return sprintf(buf, "%u\n", num_vfs); > > > } > > > /* >
