Re: [Intel-wired-lan] [PATCH v2] PCI: lock each enable/disable num_vfs operation in sysfs

[Greg]

On Fri, 2017-01-06 at 23:28 +0000, Tantilov, Emil S wrote:
> >-----Original Message-----
> >From: Intel-wired-lan [mailto:intel-wired-lan-bounces@xxxxxxxxxxxxxxxx] On
> >Behalf Of Greg
> >Sent: Friday, January 06, 2017 3:18 PM
> >To: Tantilov, Emil S <emil.s.tantilov@xxxxxxxxx>
> >Cc: linux-pci@xxxxxxxxxxxxxxx; intel-wired-lan@xxxxxxxxxxxxxxxx; linux-
> >kernel@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> >Subject: Re: [Intel-wired-lan] [PATCH v2] PCI: lock each enable/disable
> >num_vfs operation in sysfs
> >
> >On Fri, 2017-01-06 at 13:59 -0800, Emil Tantilov wrote:
> >> Enabling/disabling SRIOV via sysfs by echo-ing multiple values
> >> simultaneously:
> >>
> >> echo 63 > /sys/class/net/ethX/device/sriov_numvfs&
> >> echo 63 > /sys/class/net/ethX/device/sriov_numvfs
> >>
> >> sleep 5
> >>
> >> echo 0 > /sys/class/net/ethX/device/sriov_numvfs&
> >> echo 0 > /sys/class/net/ethX/device/sriov_numvfs
> >>
> >> Results in the following bug:
> >>
> >> kernel BUG at drivers/pci/iov.c:495!
> >> invalid opcode: 0000 [#1] SMP
> >> CPU: 1 PID: 8050 Comm: bash Tainted: G   W   4.9.0-rc7-net-next #2092
> >> RIP: 0010:[<ffffffff813b1647>]
> >> 	  [<ffffffff813b1647>] pci_iov_release+0x57/0x60
> >>
> >> Call Trace:
> >>  [<ffffffff81391726>] pci_release_dev+0x26/0x70
> >>  [<ffffffff8155be6e>] device_release+0x3e/0xb0
> >>  [<ffffffff81365ee7>] kobject_cleanup+0x67/0x180
> >>  [<ffffffff81365d9d>] kobject_put+0x2d/0x60
> >>  [<ffffffff8155bc27>] put_device+0x17/0x20
> >>  [<ffffffff8139c08a>] pci_dev_put+0x1a/0x20
> >>  [<ffffffff8139cb6b>] pci_get_dev_by_id+0x5b/0x90
> >>  [<ffffffff8139cca5>] pci_get_subsys+0x35/0x40
> >>  [<ffffffff8139ccc8>] pci_get_device+0x18/0x20
> >>  [<ffffffff8139ccfb>] pci_get_domain_bus_and_slot+0x2b/0x60
> >>  [<ffffffff813b09e7>] pci_iov_remove_virtfn+0x57/0x180
> >>  [<ffffffff813b0b95>] pci_disable_sriov+0x65/0x140
> >>  [<ffffffffa00a1af7>] ixgbe_disable_sriov+0xc7/0x1d0 [ixgbe]
> >>  [<ffffffffa00a1e9d>] ixgbe_pci_sriov_configure+0x3d/0x170 [ixgbe]
> >>  [<ffffffff8139d28c>] sriov_numvfs_store+0xdc/0x130
> >> ...
> >> RIP  [<ffffffff813b1647>] pci_iov_release+0x57/0x60
> >>
> >> Use the existing mutex lock to protect each enable/disable operation.
> >>
> >> -v2: move the existing lock from protecting the config of the IOV bus
> >> to protecting the writes to sriov_numvfs in sysfs without maintaining
> >> a "locked" version of pci_iov_add/remove_virtfn().
> >> As suggested by Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx>
> >>
> >> CC: Alexander Duyck <alexander.h.duyck@xxxxxxxxx>
> >> Signed-off-by: Emil Tantilov <emil.s.tantilov@xxxxxxxxx>
> >> ---
> >>  drivers/pci/iov.c       |    7 -------
> >>  drivers/pci/pci-sysfs.c |   23 ++++++++++++++++-------
> >>  drivers/pci/pci.h       |    2 +-
> >>  3 files changed, 17 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> >> index 4722782..2479ae8 100644
> >> --- a/drivers/pci/iov.c
> >> +++ b/drivers/pci/iov.c
> >> @@ -124,7 +124,6 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id,
> >int reset)
> >>  	struct pci_sriov *iov = dev->sriov;
> >>  	struct pci_bus *bus;
> >>
> >> -	mutex_lock(&iov->dev->sriov->lock);
> >>  	bus = virtfn_add_bus(dev->bus, pci_iov_virtfn_bus(dev, id));
> >>  	if (!bus)
> >>  		goto failed;
> >> @@ -162,7 +161,6 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id,
> >int reset)
> >>  		__pci_reset_function(virtfn);
> >>
> >>  	pci_device_add(virtfn, virtfn->bus);
> >> -	mutex_unlock(&iov->dev->sriov->lock);
> >>
> >>  	pci_bus_add_device(virtfn);
> >>  	sprintf(buf, "virtfn%u", id);
> >> @@ -181,12 +179,10 @@ int pci_iov_add_virtfn(struct pci_dev *dev, int id,
> >int reset)
> >>  	sysfs_remove_link(&dev->dev.kobj, buf);
> >>  failed1:
> >>  	pci_dev_put(dev);
> >> -	mutex_lock(&iov->dev->sriov->lock);
> >>  	pci_stop_and_remove_bus_device(virtfn);
> >>  failed0:
> >>  	virtfn_remove_bus(dev->bus, bus);
> >>  failed:
> >> -	mutex_unlock(&iov->dev->sriov->lock);
> >>
> >>  	return rc;
> >>  }
> >> @@ -195,7 +191,6 @@ void pci_iov_remove_virtfn(struct pci_dev *dev, int
> >id, int reset)
> >>  {
> >>  	char buf[VIRTFN_ID_LEN];
> >>  	struct pci_dev *virtfn;
> >> -	struct pci_sriov *iov = dev->sriov;
> >>
> >>  	virtfn = pci_get_domain_bus_and_slot(pci_domain_nr(dev->bus),
> >>  					     pci_iov_virtfn_bus(dev, id),
> >> @@ -218,10 +213,8 @@ void pci_iov_remove_virtfn(struct pci_dev *dev, int
> >id, int reset)
> >>  	if (virtfn->dev.kobj.sd)
> >>  		sysfs_remove_link(&virtfn->dev.kobj, "physfn");
> >>
> >> -	mutex_lock(&iov->dev->sriov->lock);
> >>  	pci_stop_and_remove_bus_device(virtfn);
> >>  	virtfn_remove_bus(dev->bus, virtfn->bus);
> >> -	mutex_unlock(&iov->dev->sriov->lock);
> >>
> >>  	/* balance pci_get_domain_bus_and_slot() */
> >>  	pci_dev_put(virtfn);
> >> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> >> index 0666287..25d010d 100644
> >> --- a/drivers/pci/pci-sysfs.c
> >> +++ b/drivers/pci/pci-sysfs.c
> >> @@ -472,6 +472,7 @@ static ssize_t sriov_numvfs_store(struct device *dev,
> >>  				  const char *buf, size_t count)
> >>  {
> >>  	struct pci_dev *pdev = to_pci_dev(dev);
> >> +	struct pci_sriov *iov = pdev->sriov;
> >>  	int ret;
> >>  	u16 num_vfs;
> >>
> >> @@ -482,38 +483,46 @@ static ssize_t sriov_numvfs_store(struct device
> >*dev,
> >>  	if (num_vfs > pci_sriov_get_totalvfs(pdev))
> >>  		return -ERANGE;
> >>
> >> +	mutex_lock(&iov->dev->sriov->lock);
> >> +
> >>  	if (num_vfs == pdev->sriov->num_VFs)
> >> -		return count;		/* no change */
> >> +		goto exit;
> >>
> >>  	/* is PF driver loaded w/callback */
> >>  	if (!pdev->driver || !pdev->driver->sriov_configure) {
> >>  		dev_info(&pdev->dev, "Driver doesn't support SRIOV
> >configuration via sysfs\n");
> >> -		return -ENOSYS;
> >> +		ret = -ENOENT;
> >> +		goto exit;
> >
> >Hi Emil,
> >
> >Generally the patch looks fine to me - but I am wondering why the change
> >from -ENOSYS TO -ENOENT?
> 
> Because checkpatch was complaining that ENOSYS should only be used for 
> "invalid syscall nr".
> 
> If you look at the discussion of the previous version of the patch you can
> see the details there. Basically Gavin preferred ENOENT and I don't really 
> care so much (I kind of ran into this by accident as this patch does not need
> to change the error code).

Ah, OK.  Thanks for the explanation!  Tell all my old buddies there at
Intel I said hi.

Regards,

- Greg

> 
> Thanks,
> Emil