linux-kernel - Re: [Letux-kernel] BUG: drivers/pinctrl/core: races in pinctrl

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Date:   Mon, 18 Jun 2018 21:34:08 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Christ van Willegen <cvwillegen@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        kernel@...a-handheld.com,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [Letux-kernel] BUG: drivers/pinctrl/core: races in
 pinctrl_groups and deferred probing

* H. Nikolaus Schaller <hns@...delico.com> [180618 18:33]:
> >> So code just needs group cleanup on failed probing and fixing the mutex around pinctrl_generic_add_group().
> >> 
> >> I think we need the mutex because a race still can happen when create_pinctrl() is calling pcs_dt_node_to_map()
> >> and pinctrl_generic_add_group() w/o being locked on pinctrl_maps_mutex.
> >> 
> >> The race I suspect is that two drivers are trying to insert the same name and may come
> >> both to the conclusion that it does not yet exist. And both insert into the radix tree.
> >> 
> >> The window of risk is small though... It is in pinctrl_generic_add_group() between calling
> >> pinctrl_generic_group_name_to_selector() and radix_tree_insert() so we probably won't
> >> see it in real hardware tests.
> > 
> > Hmm but that race should be already fixed with mutex held
> > by the pin controller drivers with these fixes? Or am I
> > missing something still?
> 
> Hm. Maybe we refer to a different mutex?

Yes I think that's the case, you're talking about a different
mutex here :)

> I had seen the call sequence
> 
> create_pinctrl()-> pinctrl_dt_to_map() -> pcs_dt_node_to_map() -> pinctrl_generic_add_group()
> 
> w/o any lock inside.
> 
> There is a mutex_lock(&pinctrl_maps_mutex); in create_pinctrl(), but locked after that.
> 
> Or is there a lock outside of create_pinctrl()?
> 
> If I look into the stack dumps, call nesting is
> 
> driver_probe_device() -> pinctrl_bind_pins() -> devm_pinctrl_get() -> create_pinctrl()
> 
> They all do no locking.
> 
> Maybe I am missing something.

Can you please post a patch for that as you already have it
debugged? That's easier to understand than reading a verbal
patch :)

Regards,

Tony