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From:   =?UTF-8?q?Pierre=20Cr=C3=A9gut?= <pierre.cregut@orange.com>
To:     bhelgaas@google.com
Cc:     linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        =?UTF-8?q?Pierre=20Cr=C3=A9gut?= <pierre.cregut@orange.com>
Subject: [PATCH] PCI/IOV: update num_VFs earlier
Date:   Fri, 29 Mar 2019 09:00:58 +0100
Message-Id: <20190329080058.21736-1-pierre.cregut@orange.com>
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Sender: linux-kernel-owner@vger.kernel.org
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Ensure that iov->num_VFs is set before a netlink message is sent
when the number of VFs is changed. Only the path for num_VFs > 0
is affected. The path for num_VFs = 0 is already correct.

Monitoring programs can relie on netlink messages to track interface
change and query their state in /sys. But when sriov_numvfs is set to a
positive value, the netlink message is sent before the value is available
in sysfs. The value read after the message is received is always zero.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=202991
Signed-off-by: Pierre Crégut <pierre.cregut@orange.com>
---
note: the behaviour can be tested with the following shell script also
available on the bugzilla (d being the phy device name):

ip monitor dev $d | grep --line-buffered "^[0-9]*:" | \
while read line; do cat /sys/class/net/$d/device/sriov_numvfs; done

 drivers/pci/iov.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 3aa115ed3a65..a9655c10e87f 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -351,6 +351,7 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 		goto err_pcibios;
 	}
 
+	iov->num_VFs = nr_virtfn;
 	pci_iov_set_numvfs(dev, nr_virtfn);
 	iov->ctrl |= PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE;
 	pci_cfg_access_lock(dev);
@@ -363,7 +364,6 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 		goto err_pcibios;
 
 	kobject_uevent(&dev->dev.kobj, KOBJ_CHANGE);
-	iov->num_VFs = nr_virtfn;
 
 	return 0;
 
@@ -379,6 +379,7 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	if (iov->link != dev->devfn)
 		sysfs_remove_link(&dev->dev.kobj, "dep_link");
 
+	iov->num_VFs = 0;
 	pci_iov_set_numvfs(dev, 0);
 	return rc;
 }
-- 
2.17.1