netdev - Re: [PATCH 6/7] PCI: Make sure VF's driver get attached after PF's

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Message-ID: <20130521214912.GA21713@redhat.com>
Date:	Wed, 22 May 2013 00:49:12 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Don Dutile <ddutile@...hat.com>
Cc:	Alexander Duyck <alexander.h.duyck@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Gu Zheng <guz.fnst@...fujitsu.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	NetDev <netdev@...r.kernel.org>
Subject: Re: [PATCH 6/7] PCI: Make sure VF's driver get attached after PF's

On Tue, May 21, 2013 at 05:30:32PM -0400, Don Dutile wrote:
> On 05/14/2013 05:39 PM, Alexander Duyck wrote:
> >On 05/14/2013 12:59 PM, Yinghai Lu wrote:
> >>On Tue, May 14, 2013 at 12:45 PM, Alexander Duyck
> >><alexander.h.duyck@...el.com>  wrote:
> >>>On 05/14/2013 11:44 AM, Yinghai Lu wrote:
> >>>>On Tue, May 14, 2013 at 9:00 AM, Alexander Duyck
> >>>><alexander.h.duyck@...el.com>  wrote:
> >>>>>I'm sorry, but what is the point of this patch?  With device assignment
> >>>>>it is always possible to have VFs loaded and the PF driver unloaded
> >>>>>since you cannot remove the VFs if they are assigned to a VM.
> >>>>unload PF driver will not call pci_disable_sriov?
> >>>You cannot call pci_disable_sriov because you will panic all of the
> >>>guests that have devices assigned.
> >>ixgbe_remove did call pci_disable_sriov...
> >>
> >>for guest panic, that is another problem.
> >>just like you pci passthrough with real pci device and hotremove the
> >>card in host.
> >>
> >>...
> >
> >I suggest you take another look.  In ixgbe_disable_sriov, which is the
> >function that is called we do a check for assigned VFs.  If they are
> >assigned then we do not call pci_disable_sriov.
> >
> >>
> >>>So how does your patch actually fix this problem?  It seems like it is
> >>>just avoiding it.
> >>yes, until the first one is done.
> >
> >Avoiding the issue doesn't fix the underlying problem and instead you
> >are likely just introducing more bugs as a result.
> >
> >>> From what I can tell your problem is originating in pci_call_probe.  I
> >>>believe it is calling work_on_cpu and that doesn't seem correct since
> >>>the work should be taking place on a CPU already local to the PF. You
> >>>might want to look there to see why you are trying to schedule work on a
> >>>CPU which should be perfectly fine for you to already be doing your work on.
> >>it always try to go with local cpu with same pxm.
> >
> >The problem is we really shouldn't be calling work_for_cpu in this case
> >since we are already on the correct CPU.  What probably should be
> >happening is that pci_call_probe should be doing a check to see if the
> >current CPU is already contained within the device node map and if so
> >just call local_pci_probe directly.  That way you can avoid deadlocking
> >the system by trying to flush the CPU queue of the CPU you are currently on.
> >
> That's the patch that Michael Tsirkin posted for a fix,
> but it was noted that if you have the case where the _same_ driver is used for vf & pf,
> other deadlocks may occur.
> It would work in the case of ixgbe/ixgbevf, but not for something like
> the Mellanox pf/vf driver (which is the same).
> 

I think our conclusion was this is a false positive for Mellanox.
If not, we need to understand what the deadlock is better.

> >
> >Alex
> >--
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