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

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Message-ID: <5192AEF4.1070905@intel.com>
Date:	Tue, 14 May 2013 14:39:00 -0700
From:	Alexander Duyck <alexander.h.duyck@...el.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	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 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.

Thanks,

Alex
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