linux-kernel - Re: [PATCH net v2] net/mlx5: Avoid deadlock between PCI error recovery and health reporter

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Message-ID: <3347624899623b430d62d94abcf870dac7354e0a.camel@linux.ibm.com>
Date: Wed, 08 Oct 2025 18:46:45 +0200
From: Gerd Bayer <gbayer@...ux.ibm.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Tariq Toukan <tariqt@...dia.com>, Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky	 <leon@...nel.org>, Shay Drori <shayd@...dia.com>,
        Mark
 Bloch <mbloch@...dia.com>, Andrew Lunn <andrew+netdev@...n.ch>,
        "David S .
 Miller" <davem@...emloft.net>,
        Eric Dumazet	 <edumazet@...gle.com>, Jakub
 Kicinski <kuba@...nel.org>,
        Paolo Abeni	 <pabeni@...hat.com>, Alex Vesker
 <valex@...lanox.com>,
        Feras Daoud	 <ferasda@...lanox.com>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Niklas Schnelle <schnelle@...ux.ibm.com>, linux-s390@...r.kernel.org
Subject: Re: [PATCH net v2] net/mlx5: Avoid deadlock between PCI error
 recovery and health reporter

On Tue, 2025-10-07 at 13:21 -0300, Jason Gunthorpe wrote:
> On Tue, Oct 07, 2025 at 04:48:26PM +0200, Gerd Bayer wrote:
> > - task: kmcheck
> >   mlx5_unload_one() tries to acquire devlink lock while the PCI
> > error
> >   recovery code has set pdev->block_cfg_access by way of
> >   pci_cfg_access_lock()
> 
> This seems wrong, arch code shouldn't invoke the driver's error
> handler while hodling pci_dev_lock().

Seeing how powerpc's EEH is also just acquiring the device_lock while
executing the PCI error recovery call-back, I'll be investigating that
route by "demoting" pci_dev_lock() to device_lock() (i.e. not including
the blockage of PCI config accesses)

Initial tests look promising, but I need to do more experimenting and
want to check the AER path in passing, too.

> Or at least if we do want to do this the locking should be documented
> and some lockdep map should be added to pci_cfg_access_lock() and the
> normal AER path..

This change of contract sounds a lot more intrusive to device drivers -
so I'm not actually pursuing this.

> 
> Jason

Thanks, Gerd