linux-kernel - Re: [PATCH v8 1/1] gpio: add sloppy logic analyzer using polling

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Date:   Fri, 2 Jun 2023 08:57:36 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     andy.shevchenko@...il.com
Cc:     Wolfram Sang <wsa+renesas@...g-engineering.com>,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v8 1/1] gpio: add sloppy logic analyzer using polling

On Fri, Jun 2, 2023 at 8:51 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Thu, Jun 1, 2023 at 11:40 PM <andy.shevchenko@...il.com> wrote:
> > Tue, Mar 29, 2022 at 11:11:26AM +0200, Wolfram Sang kirjoitti:
> > > This is a sloppy logic analyzer using GPIOs. It comes with a script to
> > > isolate a CPU for polling. While this is definitely not a production
> > > level analyzer, it can be a helpful first view when remote debugging.
> > > Read the documentation for details.
> >
> > One note since I have done recent review and realize one issue with debugfs.
> >
> > ...
> >
> > > +     priv->debug_dir = debugfs_create_dir(devname, gpio_la_poll_debug_dir);
> >
> > If this fails with NULL...
> >
> > > +     debugfs_create_blob("meta_data", 0400, priv->debug_dir, &priv->meta);
> > > +     debugfs_create_ulong("delay_ns", 0600, priv->debug_dir, &priv->delay_ns);
> > > +     debugfs_create_ulong("delay_ns_acquisition", 0400, priv->debug_dir, &priv->acq_delay);
> > > +     debugfs_create_file_unsafe("buf_size", 0600, priv->debug_dir, priv, &fops_buf_size);
> > > +     debugfs_create_file_unsafe("capture", 0200, priv->debug_dir, priv, &fops_capture);
> > > +     debugfs_create_file_unsafe("trigger", 0200, priv->debug_dir, priv, &fops_trigger);
> >
> > ...and any of these is not, we will end up with the file in a root folder of debugfs...
> >
> > > +     dev_info(dev, "initialized");
> >
> > ...
> >
> > > +static int gpio_la_poll_remove(struct platform_device *pdev)
> > > +{
> > > +     struct gpio_la_poll_priv *priv = platform_get_drvdata(pdev);
> > > +
> > > +     mutex_lock(&priv->lock);
> > > +     debugfs_remove_recursive(priv->debug_dir);
> >
> > ...and this one won't remove it.
> >
> > > +     mutex_unlock(&priv->lock);
> > > +     mutex_destroy(&priv->lock);
> > > +
> > > +     return 0;
> > > +}
> >
> > ...
> >
> > However, I haven't checked if it's pure theoretical issue with the current code
> > base of debugfs or a potential problem. Easy fix is to check an error code and
>
> I think debugfs_create_dir() can only fail reasonably due to OOM.

Oops, you were talking about NULL, not an error code.
I don't think that can ever happen.
And if I did miss something, it would crash when dereferencing a NULL
pointer in d_really_is_positive() (as called in start_creating())...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds