Re: [PATCH v2 5/7] PCI: Wait 1 second between disabling VFs and clearing NumVFs

From: Wei Yang
Date: Mon Nov 02 2015 - 21:02:05 EST

On Mon, Nov 02, 2015 at 07:46:24AM -0800, Alexander Duyck wrote:
>On 11/02/2015 12:33 AM, Wei Yang wrote:
>>On Fri, Oct 30, 2015 at 08:57:17AM -0700, Alexander Duyck wrote:
>>>On 10/29/2015 11:00 PM, ethan zhao wrote:
>>>>On 2015/10/30 13:14, Wei Yang wrote:
>>>>>On Thu, Oct 29, 2015 at 05:23:22PM -0500, Bjorn Helgaas wrote:
>>>>>>From: Alexander Duyck <aduyck@xxxxxxxxxxxx>
>>>>>>Per sec of the SR-IOV spec, r1.1, we must allow 1.0s after
>>>>>>VF Enable before reading any field in the SR-IOV Extended Capability.
>>>>>>Wait 1 second before calling pci_iov_set_numvfs(), which reads
>>>>>>[bhelgaas: split to separate patch for reviewability, add spec
>>>>>>Signed-off-by: Alexander Duyck <aduyck@xxxxxxxxxxxx>
>>>>>>Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>>>>>>drivers/pci/iov.c | 2 +-
>>>>>>1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>>>>>index fada98d..24428d5 100644
>>>>>>--- a/drivers/pci/iov.c
>>>>>>+++ b/drivers/pci/iov.c
>>>>>>@@ -339,13 +339,13 @@ failed:
>>>>>> iov->ctrl &= ~(PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE);
>>>>>> pci_cfg_access_lock(dev);
>>>>>> pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
>>>>>>- pci_iov_set_numvfs(dev, 0);
>>>>>> ssleep(1);
>>>>>> pci_cfg_access_unlock(dev);
>>>>>> if (iov->link != dev->devfn)
>>>>>> sysfs_remove_link(&dev->dev.kobj, "dep_link");
>>>>>>+ pci_iov_set_numvfs(dev, 0);
>>>>>One small question, any specific reason put it here instead of just after
>>>>Agree, pci_iov_set_numvfs(dev, 0) should be put before
>>>>pci_cfg_access_unlock(dev) to avoid race, because "NumVFs may only be
>>>>written while VF Enable is Clear"
>>>We are already guaranteeing that aren't we? I'm assuming there is already
>>>code in place here somewhere that prevents us from both enabling and
>>>disabling SR-IOV from more than one thread. Otherwise how could we hope to
>>>have any sort of consistent state?
>>>I'm fine with us being more explicit about it if we want to be, but if we are
>>>going to do it we should probably update all 3 spots where we update NumVFs
>>>after init instead of just this one. Perhaps it should be a separate patch.
>>Yep, I think the statement is met, "NumVFs may only be written while VF Enable
>>is Clear".
>>While in your commit log, the purpose of this patch is to wait 1 second before
>>write NumVFs. So I am interesting to know why you move this out of the
>>pci_cfg_access_lock. Because it looks better? have better performance?
>>Actually, this is a question instead of a challenge :-)
>It is because the first call to pci_iov_set_numvfs is done outside of the
>pci_cfg_access_lock. This way when I add the clean-up for the bus numbering
>failure in patch 7 I don't have to modify as much code either since the write
>is already pulled out.
>An added bonus is the code is now much closer to what we have in
>sriov_disable which has seen much more use than the exception handling case
>for sriov_enable, so it has been more thoroughly tested.

Thanks~ I am more comfortable with this change~

>- Alex

Richard Yang
Help you, Help me

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at