linux-kernel - Re: [PATCH 3/3] i2c: muxes: i2c-mux-gpmux: Use of_get_i2c_adapter_by

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Date:   Thu, 19 Oct 2023 11:46:08 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...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>
Subject: Re: [PATCH 3/3] i2c: muxes: i2c-mux-gpmux: Use
 of_get_i2c_adapter_by_node()

Hi Peter,

On Thu, 19 Oct 2023 11:26:41 +0200
Peter Rosin <peda@...ntia.se> wrote:

> Hi!
> 
> 2023-10-19 at 09:35, Herve Codina wrote:
> > i2c-mux-gpmux uses the pair of_find_i2c_adapter_by_node() /
> > i2c_put_adapter(). These pair alone is not correct to properly lock the
> > I2C parent adapter.
> > 
> > Indeed, i2c_put_adapter() decrements the module refcount while
> > of_find_i2c_adapter_by_node() does not increment it. This leads to an
> > overflow over zero of the parent adapter user counter.  
> 
> Perhaps "... underflow of the parent module refcount."?

Yes, will be changed in the next iteration.

> 
> > 
> > Use the dedicated function, of_get_i2c_adapter_by_node(), to handle
> > correctly the module refcount.
> > 
> > Signed-off-by: Herve Codina <herve.codina@...tlin.com>  
> 
> Good find, and sorry about that!
> 
> Fixes: ac8498f0ce53 ("i2c: i2c-mux-gpmux: new driver")
> Acked-by: Peter Rosin <peda@...ntia.se>

Will be added in the next iteration.

Thanks for the review,
Hervé