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

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Date:   Tue, 5 Jul 2022 18:26:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Hsin-Yi Wang <hsinyi@...omium.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 05, 2022 at 11:58:52PM +0800, Hsin-Yi Wang wrote:
> On Tue, Jul 5, 2022 at 7:51 PM Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> >
> > On Tue, Jul 05, 2022 at 07:06:41PM +0800, Hsin-Yi Wang wrote:
> > > 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.
> >
> > And how is this codepath being called if pm_genpd is not created yet?
> > Surely you are not relying on the presence of a debugfs file to
> > determine that?
> >
> 
> Caller didn't directly call genpd_debug_remove(). The flow is as follows:
> 
> Normally, scpsys will create pm domain by:
> scpsys_probe()
>    --> scpsys_add_one_domain()
>      --> pm_genpd_init()
>        --> genpd_debug_add()
> 
> 
> If something fails, it will do the cleanup:
> scpsys_probe()
>   --> scpsys_domain_cleanup()
>      --> scpsys_remove_one_domain()
>        --> pm_genpd_remove()
>           --> genpd_remove()
>             --> genpd_debug_remove()
> 
> genpd_debug_add() checks if genpd_debugfs_dir is init by a
> late_initcall genpd_debug_init(). If it's NULL, it will return
> directly without creating anything. Later when genpd_debug_init() is
> called, it will call genpd_debug_add() again.
> 
> pm_genpd_remove() still needs to be called on the cleanup path to free
> other stuff, but if genpd_debug_init() hasn't happened,
> genpd_debug_remove() should be a no-op, or genpd_remove() shouldn't
> call it. (We can move the check there, but adding in
> genpd_debug_remove() is more similar to what genpd_debug_add()
> currently is.)

Thanks for the details.  You might want to include this in the changelog
text.  I'm ok with the change now if that information is in there, I
missed that there are paths to create devices before debugfs is
initialized.

thanks,

greg k-h