netdev - Re: [PATCH iwl-next] ice: store VF's pci_dev ptr in ice

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Message-ID: <20230821110146.GA6583@unreal>
Date: Mon, 21 Aug 2023 14:01:46 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	Mateusz Polchlopek <mateusz.polchlopek@...el.com>,
	Jacob Keller <jacob.e.keller@...el.com>
Subject: Re: [PATCH iwl-next] ice: store VF's pci_dev ptr in ice_vf

On Mon, Aug 21, 2023 at 12:48:40PM +0200, Przemek Kitszel wrote:
> On 8/18/23 20:20, Leon Romanovsky wrote:
> > On Fri, Aug 18, 2023 at 02:20:51PM +0200, Przemek Kitszel wrote:
> > > On 8/16/23 16:31, Leon Romanovsky wrote:
> > > > On Wed, Aug 16, 2023 at 04:54:54AM -0400, Przemek Kitszel wrote:
> > > > > Extend struct ice_vf by vfdev.
> > > > > Calculation of vfdev falls more nicely into ice_create_vf_entries().
> > > > > 
> > > > > Caching of vfdev enables simplification of ice_restore_all_vfs_msi_state().
> > > > 
> > > > I see that old code had access to pci_dev * of VF without any locking
> > > > from concurrent PCI core access. How is it protected? How do you make
> > > > sure that vfdev is valid?
> > > > 
> > > > Generally speaking, it is rarely good idea to cache VF pci_dev pointers
> > > > inside driver.
> > > > 
> > > > Thanks
> > > 
> > > Overall, I do agree that ice driver, as a whole, has room for improvement in
> > > terms of synchronization, objects lifetime, and similar.
> > > 
> > > In this particular case, I don't see any reason of PCI reconfiguration
> > > during VF lifetime, but likely I'm missing something?
> > 
> > You are caching VF pointer in PF,
> 
> that's correct that the driver is PF/ice
> 
> > and you are subjected to PF lifetime
> > and not VF lifetime.
> 
> this belongs to struct ice_vf, which should have VF lifetime,
> otherwise it's already at risk

I'm not so sure about it. ICE used to use devm_* API and not explicit
kalloc/kfree calls, it is not clear anymore the lifetime scope of VF
structure.

Thanks

> 
> > 
> > Thanks
> 
> Thank you!