linux-kernel - Re: [PATCH 2/2] of: overlay: Synchronize of_overlay

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Date: Fri, 23 Feb 2024 11:35:37 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Herve Codina <herve.codina@...tlin.com>, Saravana Kannan
	 <saravanak@...gle.com>, Nuno Sa <nuno.sa@...log.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, Rob Herring <robh+dt@...nel.org>, Frank Rowand
 <frowand.list@...il.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>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, Luca Ceresoli <luca.ceresoli@...tlin.com>,
 Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 2/2] of: overlay: Synchronize of_overlay_remove() with
 the devlink removals

On Fri, 2024-02-23 at 10:45 +0100, Herve Codina wrote:
> Hi Saravana, Nuno, 
> 
> On Tue, 20 Feb 2024 16:37:05 -0800
> Saravana Kannan <saravanak@...gle.com> wrote:
> 
> ...
> > > @@ -1202,6 +1202,12 @@ int of_overlay_remove(int *ovcs_id)
> > >                 goto out;
> > >         }
> > > 
> > > +       /*
> > > +        * Wait for any ongoing device link removals before removing some
> > > of
> > > +        * nodes
> > > +        */
> > > +       device_link_wait_removal();
> > > +  
> > 
> > Nuno in his patch[1] had this "wait" happen inside
> > __of_changeset_entry_destroy(). Which seems to be necessary to not hit
> > the issue that Luca reported[2] in this patch series. Is there any
> > problem with doing that?
> 
> Is it the right place to wait ?
> 
> __of_changeset_entry_destroy() can do some of_node_put() and I am not sure
> that of_node_put() can call device_put() when the of_node refcount reachs
> zero.
> 

I don't think of_node_put() can call device_put(). At least by looking at:

https://elixir.bootlin.com/linux/v6.8-rc5/source/drivers/of/dynamic.c#L326

> If of_node_put() cannot call device_put(), I think we can wait in the
> of_changeset_destroy(). I.e. the __of_changeset_entry_destroy() caller.
>   https://elixir.bootlin.com/linux/v6.8-rc1/source/drivers/of/dynamic.c#L670
> 
> What do you think about this ?
> Does it make sense ?

I think it makes sense from a logical point of view. Like, let's flush the queue
right before checking our assumptions...

In my tests, I did not saw any issue (Hopefully I was not missing any subtlety).

- Nuno Sá