linux-kernel - Re: [PATCH] coccinelle: put_device: Include of_node

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Date:   Mon, 27 Feb 2023 01:52:49 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     nicolas palix <nicolas.palix@...g.fr>, cocci <cocci@...ia.fr>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>,
        Deepak R Varma <drv@...lo.com>
Subject: Re: [PATCH] coccinelle: put_device: Include of_node_put to avoid
 false positives

On Sat, Feb 25, 2023 at 08:17:01PM +0100, Julia Lawall wrote:
> > The node reference increased by of_find_device_by_node() can also be
> > released by using a call to of_node_put(). Hence when this exists, the
> > script should not trigger a warning, which otherwise will be a false
> > positive.
> 
> Could you explain more about why of_node_put is sufficient?

You are right. In fact, I think calling of_node_put() for a prior
of_find_device_by_node() is buggy as a call to of_find_device_by_node()
increments the kref for the device embedding the node and not the kref of the
node. Hence a call to put_device() is required to decrement the device kref.
Calling the of_node_put() attempts to decrement the kref of the node, which I
think is not correct.

May I request any comment on my understanding?

Thank you,
deepak.

> 
> thanks,
> julia
> 
> > Also, improve the warning message to include of_node_put too is missing.
> > 
> > Signed-off-by: Deepak R Varma <drv@...lo.com>
> > ---
> > scripts/coccinelle/free/put_device.cocci | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/scripts/coccinelle/free/put_device.cocci
> > b/scripts/coccinelle/free/put_device.cocci
> > index f09f1e79bfa6..259195b501aa 100644
> > --- a/scripts/coccinelle/free/put_device.cocci
> > +++ b/scripts/coccinelle/free/put_device.cocci
> > @@ -18,8 +18,10 @@ type T,T1,T2,T3;
> > 
> > id = of_find_device_by_node@p1(x)
> > ... when != e = id
> > +    when != of_node_put(x)
> > if (id == NULL || ...) { ... return ...; }
> > ... when != put_device(&id->dev)
> > +    when != of_node_put(x)
> >     when != platform_device_put(id)
> >     when != if (id) { ... put_device(&id->dev) ... }
> >     when != e1 = (T)id
> > @@ -42,7 +44,7 @@ p2 << search.p2;
> > @@
> > 
> > coccilib.report.print_report(p2[0],
> > -                             "ERROR: missing put_device; call
> > of_find_device_by_node on line "
> > +                             "ERROR: missing put_device or of_node_put; call
> > of_find_device_by_node on line "
> >                              + p1[0].line
> >                              + ", but without a corresponding object release within this function.")
> > 
> > --
> > 2.34.1