netdev - Re: [PATCH net-next 05/14] devlink: Acquire device lock during reload command

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Date: Fri, 17 Nov 2023 15:51:17 +0000
From: Simon Horman <horms@...nel.org>
To: Petr Machata <petrm@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org, Ido Schimmel <idosch@...dia.com>,
	Amit Cohen <amcohen@...dia.com>, mlxsw@...dia.com,
	Jiri Pirko <jiri@...dia.com>
Subject: Re: [PATCH net-next 05/14] devlink: Acquire device lock during
 reload command

On Wed, Nov 15, 2023 at 01:17:14PM +0100, Petr Machata wrote:
> From: Ido Schimmel <idosch@...dia.com>
> 
> Device drivers register with devlink from their probe routines (under
> the device lock) by acquiring the devlink instance lock and calling
> devl_register().
> 
> Drivers that support a devlink reload usually implement the
> reload_{down, up}() operations in a similar fashion to their remove and
> probe routines, respectively.
> 
> However, while the remove and probe routines are invoked with the device
> lock held, the reload operations are only invoked with the devlink
> instance lock held. It is therefore impossible for drivers to acquire
> the device lock from their reload operations, as this would result in
> lock inversion.
> 
> The motivating use case for invoking the reload operations with the
> device lock held is in mlxsw which needs to trigger a PCI reset as part
> of the reload. The driver cannot call pci_reset_function() as this
> function acquires the device lock. Instead, it needs to call
> __pci_reset_function_locked which expects the device lock to be held.
> 
> To that end, adjust devlink to always acquire the device lock before the
> devlink instance lock when performing a reload.
> 
> Do that when reload is explicitly triggered by user space by specifying
> the 'DEVLINK_NL_FLAG_NEED_DEV_LOCK' flag in the pre_doit and post_doit
> operations of the reload command.
> 
> A previous patch already handled the case where reload is invoked as
> part of netns dismantle.
> 
> Signed-off-by: Ido Schimmel <idosch@...dia.com>
> Reviewed-by: Jiri Pirko <jiri@...dia.com>
> Signed-off-by: Petr Machata <petrm@...dia.com>

Reviewed-by: Simon Horman <horms@...nel.org>