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Message-ID: <519D3B61.5030700@redhat.com> Date: Wed, 22 May 2013 17:40:49 -0400 From: Don Dutile <ddutile@...hat.com> To: Or Gerlitz <or.gerlitz@...il.com> CC: Alexander Duyck <alexander.duyck@...il.com>, "Michael S. Tsirkin" <mst@...hat.com>, 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>, Jack Morgenstein <jackm@....mellanox.co.il> Subject: Re: [PATCH 6/7] PCI: Make sure VF's driver get attached after PF's On 05/22/2013 04:16 PM, Or Gerlitz wrote: > On Wed, May 22, 2013 at 1:30 AM, Alexander Duyck > <alexander.duyck@...il.com> wrote: >> On 05/21/2013 03:11 PM, Michael S. Tsirkin wrote: >>> On Tue, May 21, 2013 at 03:01:08PM -0700, Alexander Duyck wrote: >>>> On 05/21/2013 02:49 PM, Michael S. Tsirkin wrote: >>>>> 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. >>>>> >>>> >>>> As I understand the issue, the problem is not a deadlock for Mellanox >>>> (At least with either your patch or mine applied), the issue is that the >>>> PF is not ready to handle VFs when pci_enable_sriov is called due to >>>> some firmware issues. > > >>> I haven't seen Mellanox guys say anything like this on the list. Pointers? >>> All I saw is some lockdep warnings and Tejun says they are bogus ... >> >> Actually the patch I submitted is at: >> https://patchwork.kernel.org/patch/2568881/ >> >> It was in response to: >> https://patchwork.kernel.org/patch/2562471/ >> >> Basically the patch I was responding to was supposed to address both the >> lockdep issue and a problem with mlx4 not being able to support the VFs >> when pci_enable_sriov is called. Yinghai had specifically called out >> the work_on_cpu lockdep issue that you also submitted a patch for. >> >> As per the feedback from Yinghai it seems like my patch does resolve the >> lockdep issue that was seen. The other half of the issue was what we >> have been discussing with Or in regards to delaying VF driver init via >> something like -EPROBE_DEFER instead of trying to split up >> pci_enable_sriov and VF probe. > > > Hi Alex, all, so to clarify: > > 1. currently due to current firmware limitation we must call > pci_enable_sriov before the > PF ends its initialization sequence done in the PCI probe callback, hence > > 2. we can't move to the new sysfs API for enabling SRIOV > > 3. as of 3.9-rc1 we see these nested brobes, bisected that to be as of > commit 90888ac01d059e38ffe77a2291d44cafa9016fb "driver core: fix > possible missing of device probe". But we didn't reach into consensus > with the author that this wasn't possible before the commit, nor this > is something that needs to be avoided, see > http://marc.info/?t=136249697200007&r=1&w=2 > > 4. I am not sure if/how we can modify the PF code to support the case > where VFs are probed and start thier initialization sequence before > the PF is done with its initialization > > 5. etc > > all in all, we will look into returning -EPROBE_DEFER from the VF > when they identify the problematic situation -- so for how much time > this is deferred? or if this isn't time based what the logical > condition which once met the VF probe is attempted again? > ah, sounds device specific.... i.e., it goes back to PF probe.... So, I'm assuming some sort of init/info-xchg is done btwn VF & PF and has to be done to some level before PF can continue it's pci-probe operation. In that case, has the VF & PF done sufficient init/info-xchg on 1st call, that the PF can continue, and then queue up a sriov-enable at the end of PF probe ? > > Or. > -- > To unsubscribe from this list: send the line "unsubscribe linux-pci" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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