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Date: Mon, 25 Mar 2024 19:37:10 +0100
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Herve Codina <herve.codina@bootlin.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Saravana Kannan <saravanak@google.com>,
	Lizhi Hou <lizhi.hou@amd.com>, Max Zhen <max.zhen@amd.com>,
	Sonal Santan <sonal.santan@amd.com>,
	Stefano Stabellini <stefano.stabellini@xilinx.com>,
	Jonathan Cameron <Jonathan.Cameron@huawei.com>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	Allan Nielsen <allan.nielsen@microchip.com>,
	Horatiu Vultur <horatiu.vultur@microchip.com>,
	Steen Hegelund <steen.hegelund@microchip.com>,
	Luca Ceresoli <luca.ceresoli@bootlin.com>,
	Nuno Sa <nuno.sa@analog.com>,
	Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v6 1/2] driver core: Introduce device_link_wait_removal()
Message-ID: <2024032548-rope-improper-4f67@gregkh>
References: <20240325152140.198219-1-herve.codina@bootlin.com>
 <20240325152140.198219-2-herve.codina@bootlin.com>
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In-Reply-To: <20240325152140.198219-2-herve.codina@bootlin.com>

On Mon, Mar 25, 2024 at 04:21:25PM +0100, Herve Codina wrote:
> The commit 80dd33cf72d1 ("drivers: base: Fix device link removal")
> introduces a workqueue to release the consumer and supplier devices used
> in the devlink.
> In the job queued, devices are release and in turn, when all the
> references to these devices are dropped, the release function of the
> device itself is called.
> 
> Nothing is present to provide some synchronisation with this workqueue
> in order to ensure that all ongoing releasing operations are done and
> so, some other operations can be started safely.
> 
> For instance, in the following sequence:
>   1) of_platform_depopulate()
>   2) of_overlay_remove()
> 
> During the step 1, devices are released and related devlinks are removed
> (jobs pushed in the workqueue).
> During the step 2, OF nodes are destroyed but, without any
> synchronisation with devlink removal jobs, of_overlay_remove() can raise
> warnings related to missing of_node_put():
>   ERROR: memory leak, expected refcount 1 instead of 2
> 
> Indeed, the missing of_node_put() call is going to be done, too late,
> from the workqueue job execution.
> 
> Introduce device_link_wait_removal() to offer a way to synchronize
> operations waiting for the end of devlink removals (i.e. end of
> workqueue jobs).
> Also, as a flushing operation is done on the workqueue, the workqueue
> used is moved from a system-wide workqueue to a local one.
> 
> Cc: stable@vger.kernel.org

Why is this for stable?  You are just adding a new api, no one is using
it.

Or if they are, you didn't send me that patch...

greg k-h