Re: [PATCH v10 0/2] PCI/IOV: Fix SR-IOV locking races and AB-BA deadlock

[Guenter Roeck]

On 3/19/26 05:31, Niklas Schnelle wrote:
> On Wed, 2026-03-18 at 23:03 +0200, Ionut Nechita (Wind River) wrote:
> > From: Ionut Nechita <ionut.nechita@xxxxxxxxxxxxx>
> >
> > Hi Bjorn,
> >
> > This is v10 of the fix for the SR-IOV race between driver .remove()
> > and concurrent hotplug events.  v10 adds a second patch to fix the
> > AB-BA deadlock between device_lock and pci_rescan_remove_lock that
> > was reported by Guenter Roeck (via Google's AI review agent) and
> > confirmed by Benjamin Block.
> >
> > The AB-BA deadlock:
> >
> >    CPU0 (remove_store)               CPU1 (unbind_store)
> >    --------------------              --------------------
> >    pci_lock_rescan_remove()
> >                                      device_lock()
> >                                      driver .remove()
> >                                        sriov_del_vfs()
> >                                          pci_lock_rescan_remove()  <-- WAITS
> >    pci_stop_bus_device()
> >      device_release_driver()
> >        device_lock()                                               <-- WAITS
> >
> > Patch 2/2 fixes this by calling device_release_driver() in
> > remove_store() before pci_stop_and_remove_bus_device_locked(), so
> > that the driver is already unbound when pci_rescan_remove_lock is
> > acquired. Both paths then take locks in the same order: device_lock
> > first, then pci_rescan_remove_lock.
> >
> > Note: the concurrent unbind_store + hotplug-event case (where the
> > hotplug handler takes pci_rescan_remove_lock before device_lock)
> > remains a known limitation.  This is a pre-existing issue that
> > Benjamin Block is addressing separately in:
> >    https://lore.kernel.org/linux-pci/354b9e4a54ced67f3c89df198041df19434fe4c8.1773235561.git.bblock@xxxxxxxxxxxxx/
> --- snip ---
> > Ionut Nechita (2):
> >    PCI/IOV: Make pci_lock_rescan_remove() reentrant and protect
> >      sriov_add_vfs/sriov_del_vfs
> >    PCI: Fix AB-BA deadlock between device_lock and
> >      pci_rescan_remove_lock in remove_store
> >
> >   drivers/pci/iov.c       |  9 +++++----
> >   drivers/pci/pci-sysfs.c | 20 +++++++++++++++++++-
> >   drivers/pci/probe.c     | 11 +++++++++--
> >   3 files changed, 33 insertions(+), 7 deletions(-)
> >
> > --
> > 2.43.0
>
> Hi Ionut,
>
> For your awareness, I saw that this series has some findings on
> Google's new Sashiko AI reviewing tool[0]. At a quick glance the
> findings seem like at least reasonable concerns to me. I'm still
> looking at this independently also of course.

It is almost scary to see how many problems Sashiko is able to find.
The AB-BA deadlock that the second patch in the series tries to fix
was reported by a prototype version of it when running it on an LTS
backport.

Guenter