On Fri, Feb 09, 2024 at 07:20:28PM -0800, Kuppuswamy Sathyanarayanan wrote: > > On 2/9/24 3:52 PM, Jim Harris wrote: > > If an SR-IOV enabled device is held by vfio, and the device is removed, > > vfio will hold device lock and notify userspace of the removal. If > > userspace reads the sriov_numvfs sysfs entry, that thread will be blocked > > since sriov_numvfs_show() also tries to acquire the device lock. If that > > same thread is responsible for releasing the device to vfio, it results in > > a deadlock. > > > > The proper way to detect a change to the num_VFs value is to listen for a > > sysfs event, not to add a device_lock() on the attribute _show() in the > > kernel. > > Since you are reverting a commit that synchronizes SysFS read > /write, please add some comments about why it is not an > issue anymore. It was never an issue, the idea that sysfs read and write should be serialized by kernel is not correct by definition. Thanks > > > > > This reverts commit 35ff867b76576e32f34c698ccd11343f7d616204. > > Revert had a small conflict, the sprintf() is now changed to sysfs_emit(). > > > > Link: https://lore.kernel.org/linux-pci/ZXJI5+f8bUelVXqu@ubuntu/ > > Suggested-by: Leon Romanovsky <leonro@xxxxxxxxxx> > > Reviewed-by: Leon Romanovsky <leonro@xxxxxxxxxx> > > Signed-off-by: Jim Harris <jim.harris@xxxxxxxxxxx> > > --- > > drivers/pci/iov.c | 8 +------- > > 1 file changed, 1 insertion(+), 7 deletions(-) > > > > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c > > index aaa33e8dc4c9..0ca20cd518d5 100644 > > --- a/drivers/pci/iov.c > > +++ b/drivers/pci/iov.c > > @@ -395,14 +395,8 @@ 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_unlock(&pdev->dev); > > > > - return sysfs_emit(buf, "%u\n", num_vfs); > > + return sysfs_emit(buf, "%u\n", pdev->sriov->num_VFs); > > } > > > > /* > > > -- > Sathyanarayanan Kuppuswamy > Linux Kernel Developer >
