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

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Date: Fri, 23 Feb 2024 10:45:50 +0100
From: Herve Codina <herve.codina@...tlin.com>
To: 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

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.

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 ?

> 
> Luca for some reason did a unlock/lock(of_mutex) in his test patch and
> I don't think that's necessary.
> 
> Can you move this call to where Nuno did it and see if that works for
> all of you?

I will check.

Best regards,
Hervé