linux-kernel - Re: [v6 08/14] iio: imu: add Bosch Sensortec BNO055 core driver

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Date:   Tue, 14 Jun 2022 17:27:32 +0200
From:   Andrea Merello <andrea.merello@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andrea Merello <Andrea.Merello@....it>,
        Jonathan Cameron <jic23@...nel.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Matt Ranostay <matt.ranostay@...sulko.com>,
        Alexandru Ardelean <ardeleanalex@...il.com>,
        jmondi <jacopo@...ndi.org>
Subject: Re: [v6 08/14] iio: imu: add Bosch Sensortec BNO055 core driver

Il giorno mar 14 giu 2022 alle ore 17:11 Andy Shevchenko
<andy.shevchenko@...il.com> ha scritto:
>
> On Tue, Jun 14, 2022 at 2:15 PM Andrea Merello <Andrea.Merello@....it> wrote:
>
> ...
>
> > >> >> +       devm_add_action_or_reset(priv->dev, bno055_debugfs_remove, priv->debugfs);
> > >> >
> > >> >Shouldn't we report the potential error here? It's not directly
> > >> >related to debugfs, but something which is not directly related.
> > >>
> > >> The error eventually comes out from something that has nothing to do with debugs per se (i.e. the devm stuff), but it will only affect debugfs indeed.
> > >>
> > >> Assuming that we don't want to make the whole driver fail in case debugfs stuff fails (see last part of the comment above debugfs_create_file() implementation), and given that the devm_add_action_or_reset(), should indeed "reset" in case of failure (i.e.  we should be in a clean situation anyway), I would say it should be OK not to propagate the error and let things go on.
> > >
> > >As I said, it's not directly related to debugfs. Here is the resource
> > >leak possible or bad things happen if you probe the driver, that fails
> > >to add this call for removal, remove it, and try to insert again, in
> > >such case the debugfs will be stale.
> >
> > Hum, I would say this shouldn't ever happen: AFAICS devm_add_action_or_reset() is a wrapper around devm_add_action() and it's purpose is exactly to add a check for failure; devm_add_action_or_reset() immediately invokes the action handler in case devm_add_action() fails. IOW in case of failure to add the devm stuff, the debugfs file is removed immediately and it shouldn't cause any mess with next times probe()s; just the driver will go on without the debugfs file being here.
> >
> > I think this is the point of using devm_add_action_or_reset() instead of dev_add_action()  indeed, or am I missing something?
>
> Reading that code again and I think you are right, so dev_warn() will
> be sufficient to show that we fail. OTOH, what is the point of adding
> a resource for the failed debugfs call?

Ah, you are right here: I'll make the call to
devm_add_action_or_reset() conditional to success of
debugfs_create_file(). In case any of the two fails we can also warn
the user.

> --
> With Best Regards,
> Andy Shevchenko