linux-kernel - Re: [PATCH v6 1/2] driver core: Introduce device_link_wait

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

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@...r.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