linux-kernel - Re: [PATCH v3 0/2] PCI/IOV: Fix deadlock when removing PF with enabled SR-IOV

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Message-ID: <20260203004810.GA14073@bhelgaas>
Date: Mon, 2 Feb 2026 18:48:10 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Niklas Schnelle <schnelle@...ux.ibm.com>
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
Subject: Re: [PATCH v3 0/2] PCI/IOV: Fix deadlock when removing PF with
 enabled SR-IOV

On Tue, Dec 16, 2025 at 11:14:01PM +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 v3:
> - Rebased on v6.19-rc1, also verified issue is still there and the fix
>   still works
> - Added more of the lockdep splat for better context
> - Link to v2: https://lore.kernel.org/r/20251119-revert_sriov_lock-v2-0-ea50eb1e8f96@linux.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: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
> change-id: 20251029-revert_sriov_lock-aef4557f360f

Applied to pci/iov for v6.20, thanks!