Re: [PATCH] PM: domains: Ensure genpd_debugfs_dir exists before remove

Greg Kroah-Hartman
2022-07-05T16:26:49Z

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@linuxfoundation.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@linuxfoundation.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@chromium.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