> -----Original Message----- > From: Jason Gunthorpe [mailto:jgg@xxxxxxxxxx] > Sent: 27 September 2021 16:01 > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>; > Leon Romanovsky <leonro@xxxxxxxxxx> > Cc: kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > linux-crypto@xxxxxxxxxxxxxxx; alex.williamson@xxxxxxxxxx; > mgurtovoy@xxxxxxxxxx; liulongfang <liulongfang@xxxxxxxxxx>; Zengtao (B) > <prime.zeng@xxxxxxxxxxxxx>; Jonathan Cameron > <jonathan.cameron@xxxxxxxxxx>; Wangzhou (B) <wangzhou1@xxxxxxxxxxxxx> > Subject: Re: [PATCH v3 6/6] hisi_acc_vfio_pci: Add support for VFIO live > migration > > On Mon, Sep 27, 2021 at 01:46:31PM +0000, Shameerali Kolothum Thodi > wrote: > > > > > > Nope, this is locked wrong and has no lifetime management. > > > > > > > > Ok. Holding the device_lock() sufficient here? > > > > > > You can't hold a hisi_qm pointer with some kind of lifecycle > > > management of that pointer. device_lock/etc is necessary to call > > > pci_get_drvdata() > > > > Since this migration driver only supports VF devices and the PF > > driver will not be removed until all the VF devices gets removed, > > is the locking necessary here? > > Oh.. That is really busted up. pci_sriov_disable() is called under the > device_lock(pf) and obtains the device_lock(vf). > > This means a VF driver can never use the device_lock(pf), otherwise it > can deadlock itself if PF removal triggers VF removal. Exactly. I can easily simulate that in this driver. > > But you can't access these members without using the device_lock(), as > there really are no safety guarentees.. Hmm.. I was hoping that we can avoid holding the lock since we are sure of the PF driver behavior. But right, there are no guarantee here. > The mlx5 patches have this same sketchy problem. > > We may need a new special function 'pci_get_sriov_pf_devdata()' that > confirms the vf/pf relationship and explicitly interlocks with the > pci_sriov_enable/disable instead of using device_lock() > > Leon, what do you think? > Thanks, Shameer
