linux-kernel - Re: [PATCH] PM: domains: Ensure genpd_debugfs

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Date:   Tue, 5 Jul 2022 19:06:41 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Thierry Strudel <tstrudel@...gle.com>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Pin-yen Lin <treapking@...omium.org>
Subject: Re: [PATCH] PM: domains: Ensure genpd_debugfs_dir exists before remove

On Tue, Jul 5, 2022 at 6:38 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Jul 05, 2022 at 05:49:47PM +0800, Hsin-Yi Wang wrote:
> > genpd_debug_remove() may be indirectly called from others while
> > genpd_debugfs_dir is not yet set. Make sure genpd_debugfs_dir exists
> > before remove the sub components, otherwise components under
> > /sys/kernel/debug may be accidentally removed.
> >
> > Fixes: 718072ceb211 ("PM: domains: create debugfs nodes when adding power domains")
> > Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> > ---
> > An example:
> > scpsys_probe() in drivers/soc/mediatek/mtk-pm-domains.c indirectly calls
> > genpd_debug_remove() on probe fail, causing /sys/kernel/debug/usb to be
> > removed.
> > ---
> >  drivers/base/power/domain.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> > index 3e86772d5fac5..5a2e0232862e0 100644
> > --- a/drivers/base/power/domain.c
> > +++ b/drivers/base/power/domain.c
> > @@ -222,6 +222,9 @@ static void genpd_debug_remove(struct generic_pm_domain *genpd)
> >  {
> >       struct dentry *d;
> >
> > +     if (!genpd_debugfs_dir)
> > +             return;
> > +
> >       d = debugfs_lookup(genpd->name, genpd_debugfs_dir);
> >       debugfs_remove(d);
>
> Why not just change this to be:
>         debugfs_remove(debugfs_lookup(genpd->name, debugfs_lookup("pm_genpd", NULL)));
If pm_genpd hasn't been created yet,  debugfs_lookup("pm_genpd", NULL)
will return null.
If genpd->name also exists under root debugfs, it will still be
deleted unintentionally, since NULL represents root debugfs.
Eg. one of the genpd->name is "usb", which is supposed to be added as
/sys/kernel/debug/pm_genpd/usb later. But pm_genpd is not yet created,
/sys/kernel/debug/usb will be removed.

>
> thanks,
>
> greg k-h