linux-kernel - Re: [PATCH 7/7] regulator: remove superfluous lock in regulator_resolve

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Date:   Tue, 11 Aug 2020 18:56:20 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Vladimir Zapolskiy <vz@...ia.com>
Subject: Re: [PATCH 7/7] regulator: remove superfluous lock in
 regulator_resolve_coupling()

11.08.2020 04:07, Michał Mirosław пишет:
> The code modifies rdev, but locks c_rdev instead. The bug remains:
> stored c_rdev could be freed just after unlock anyway. This doesn't blow
> up because regulator_list_mutex taken outside holds it together.
> 
> Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> ---
>  drivers/regulator/core.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
> index b85ec974944e..f8834559a2fb 100644
> --- a/drivers/regulator/core.c
> +++ b/drivers/regulator/core.c
> @@ -4942,13 +4942,9 @@ static void regulator_resolve_coupling(struct regulator_dev *rdev)
>  			return;
>  		}
>  
> -		regulator_lock(c_rdev);
> -
>  		c_desc->coupled_rdevs[i] = c_rdev;
>  		c_desc->n_resolved++;
>  
> -		regulator_unlock(c_rdev);
> -
>  		regulator_resolve_coupling(c_rdev);
>  	}
>  }
> 

As I replied to the other email, there is no real bug here. The
regulators are uncoupled before regulator is freed and the uncoupling is
also protected by the list_mutex.

Hence the resolve_coupling() doesn't need to lock regulators and this
change looks like a good cleanup.

Perhaps the commit message could be improved a tad, either way:

Reviewed-by: Dmitry Osipenko <digetx@...il.com>