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

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Wed, 2026-03-18 at 23:03 +0200, Ionut Nechita (Wind River) wrote:
> From: Ionut Nechita <ionut.nechita@windriver.com>
> 
> 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@linux.ibm.com/
> 
--- 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.

Thanks,
Niklas

[0]
https://sashiko.dev/#/patchset/20260318210316.61975-1-ionut.nechita%40windriver.com