linux-kernel - Re: [PATCH 1/3] media: ngene: Replace semaphore cmd

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Message-ID: <CAK8P3a2huLuzaaHh-hw4S1pRa0BTPEywvp3Kw134j_dm8Lns6g@mail.gmail.com>
Date:   Thu, 8 Jun 2017 17:10:51 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Binoy Jayan <binoy.jayan@...aro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Rajendra <rnayak@...eaurora.org>,
        Mark Brown <broonie@...nel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Julia Lawall <Julia.Lawall@...6.fr>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Cao jin <caoj.fnst@...fujitsu.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>
Subject: Re: [PATCH 1/3] media: ngene: Replace semaphore cmd_mutex with mutex

On Thu, Jun 8, 2017 at 12:04 PM, Binoy Jayan <binoy.jayan@...aro.org> wrote:
> The semaphore 'cmd_mutex' is used as a simple mutex, so
> it should be written as one. Semaphores are going away in the future.
>
> Signed-off-by: Binoy Jayan <binoy.jayan@...aro.org>
> ---

> @@ -1283,7 +1283,7 @@ static int ngene_load_firm(struct ngene *dev)
>
>  static void ngene_stop(struct ngene *dev)
>  {
> -       down(&dev->cmd_mutex);
> +       mutex_lock(&dev->cmd_mutex);
>         i2c_del_adapter(&(dev->channel[0].i2c_adapter));
>         i2c_del_adapter(&(dev->channel[1].i2c_adapter));
>         ngwritel(0, NGENE_INT_ENABLE);

Are you sure about this one? There is only one mutex_lock() and
then the structure gets freed without a corresponding mutex_unlock().

I suspect this violates some rules of mutexes, either when compile
testing with "make C=1", or when running with lockdep enabled.

Can we actually have a concurrently held mutex at the time we
get here? If not, using mutex_destroy() in place of the down()
may be the right answer.

       Arnd