linux-kernel - Re: [PATCH v2 0/2] PCI/IOV: Fix deadlock when removing PF with enabled SR-IOV

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Message-ID: <440934261b39a033b20063d6a598d06bb343caad.camel@linux.ibm.com>
Date: Wed, 19 Nov 2025 13:43:21 +0100
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Lukas Wunner <lukas@...ner.de>, Keith Busch <kbusch@...nel.org>,
        Gerd
 Bayer	 <gbayer@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Benjamin Block	 <bblock@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>, Farhan Ali	 <alifm@...ux.ibm.com>,
        Julian Ruess <julianr@...ux.ibm.com>,
        Heiko Carstens	 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev	 <agordeev@...ux.ibm.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        regressions <regressions@...ts.linux.dev>
Subject: Re: [PATCH v2 0/2] PCI/IOV: Fix deadlock when removing PF with
 enabled SR-IOV

On Wed, 2025-11-19 at 13:34 +0100, Niklas Schnelle wrote:
> Hi Bjorn,
> 
> Doing additional testing for a distribution backport of commit
> 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when
> enabling/disabling SR-IOV") Benjamin found a hang with s390's
> recover attribute. Further investigation showed this to be a deadlock by
> recursively trying to take pci_rescan_remove lock when removing a PF
> with enabled SR-IOV.
> 
> The issue can be reproduced on both s390 and x86_64 with:
> 
>     $ echo <NUM> > /sys/bus/pci/devices/<pf>/sriov_numvfs
>     $ echo 1 > /sys/bus/pci/devices/<pf>/remove
> 
> As this seems worse than the original, hard to hit, race fixed by the
> cited commit I think we first want to revert the broken fix.
> 
> Following that patch 2 attempts to fix the original issue by taking the
> PCI rescan/remove lock directly before calling into the driver's
> sriov_configure() callback enforcing the rule that this should only
> be called with the pci_rescan_remove_lock held.
> 
> Thanks,
> Niklas
> 
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---
> Changes in v2:
> - Collected R-b from Benjamin
> - Link to v1: https://lore.kernel.org/r/20251030-revert_sriov_lock-v1-0-70f82ade426f@linux.ibm.com
> 
> ---
> Niklas Schnelle (2):
>       Revert "PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV"
>       PCI/IOV: Fix race between SR-IOV enable/disable and hotplug
> 
>  drivers/pci/iov.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> ---
> base-commit: dcb6fa37fd7bc9c3d2b066329b0d27dedf8becaa
> change-id: 20251029-revert_sriov_lock-aef4557f360f
> 
> Best regards,

Since this is really a regression without a separate report, yet this
has a description and reproducer I'm just adding this here:

#regzbot ^introduced: 05703271c3cd