linux-kernel - Re: [PATCH v3] fpga: bridge: add owner module and take its refcount

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Date: Sun, 31 Mar 2024 21:48:52 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Marco Pagani <marpagan@...hat.com>
Cc: Moritz Fischer <mdf@...nel.org>, Wu Hao <hao.wu@...el.com>,
	Xu Yilun <yilun.xu@...el.com>, Tom Rix <trix@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Tull <atull@...nsource.altera.com>,
	Russ Weight <russ.weight@...ux.dev>, linux-fpga@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] fpga: bridge: add owner module and take its refcount

On Fri, Mar 22, 2024 at 06:18:37PM +0100, Marco Pagani wrote:
> The current implementation of the fpga bridge assumes that the low-level
> module registers a driver for the parent device and uses its owner pointer
> to take the module's refcount. This approach is problematic since it can
> lead to a null pointer dereference while attempting to get the bridge if
> the parent device does not have a driver.
> 
> To address this problem, add a module owner pointer to the fpga_bridge
> struct and use it to take the module's refcount. Modify the function for
> registering a bridge to take an additional owner module parameter and
> rename it to avoid conflicts. Use the old function name for a helper macro
> that automatically sets the module that registers the bridge as the owner.
> This ensures compatibility with existing low-level control modules and
> reduces the chances of registering a bridge without setting the owner.
> 
> Also, update the documentation to keep it consistent with the new interface
> for registering an fpga bridge.
> 
> Other changes: opportunistically move put_device() from __fpga_bridge_get()
> to fpga_bridge_get() and of_fpga_bridge_get() to improve code clarity since
> the bridge device is taken in these functions.
> 
> Fixes: 21aeda950c5f ("fpga: add fpga bridge framework")
> Suggested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Suggested-by: Xu Yilun <yilun.xu@...el.com>
> Reviewed-by: Russ Weight <russ.weight@...ux.dev>
> Signed-off-by: Marco Pagani <marpagan@...hat.com>

Acked-by: Xu Yilun <yilun.xu@...el.com>

Applied to for-next.