linux-kernel - Re: [PATCH] PCI: Fix devres regression in pci

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Message-ID: <20240903094431.63551744.alex.williamson@redhat.com>
Date: Tue, 3 Sep 2024 09:44:31 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Philipp Stanner <pstanner@...hat.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, Krzysztof Wilczyński <kwilczynski@...nel.org>, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org, Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [PATCH] PCI: Fix devres regression in pci_intx()

On Thu, 25 Jul 2024 14:07:30 +0200
Philipp Stanner <pstanner@...hat.com> wrote:

> pci_intx() is a function that becomes managed if pcim_enable_device()
> has been called in advance. Commit 25216afc9db5 ("PCI: Add managed
> pcim_intx()") changed this behavior so that pci_intx() always leads to
> creation of a separate device resource for itself, whereas earlier, a
> shared resource was used for all PCI devres operations.
> 
> Unfortunately, pci_intx() seems to be used in some drivers' remove()
> paths; in the managed case this causes a device resource to be created
> on driver detach.
> 
> Fix the regression by only redirecting pci_intx() to its managed twin
> pcim_intx() if the pci_command changes.
> 
> Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()")

I'm seeing another issue from this, which is maybe a more general
problem with managed mode.  In my case I'm using vfio-pci to assign an
ahci controller to a VM.  ahci_init_one() calls pcim_enable_device()
which sets is_managed = true.  I notice that nothing ever sets
is_managed to false.  Therefore now when I call pci_intx() from vfio-pci
under spinlock, I get a lockdep warning as I no go through pcim_intx()
code after 25216afc9db5 since the previous driver was managed.  It seems
like we should be setting is_managed to false is the driver release
path, right?  Thanks,

Alex