Messages in this thread | | | From | Hsin-Yi Wang <> | Date | Tue, 5 Jul 2022 23:58:52 +0800 | Subject | Re: [PATCH] PM: domains: Ensure genpd_debugfs_dir exists before remove |
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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.)
> > 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. > > Ah, that's a bad name to pick :) > > But still, don't paper over this problem, please solve the root issue of > never relying on the creation of a debugfs file to determine functional > logic. > Currently we can't remove genpd_debug_add() called in pm_genpd_init() and genpd_debug_remove() called in genpd_remove(). If some power domain is created after genpd_debug_init(), their genpd subdomain won't be registered in debugfs. genpd_debug_remove() also has similar issues, eg. failed domain not removed after genpd_debug_init() is called.
> thanks, > > greg k-h
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