linux-kernel - Re: [PATCH] gpiolib: don't call sleeping functions with a spinlock taken

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Message-ID: <CAMpxmJVT4wm26hQB-_BV73tC5_nqH5JG9KmDuNQ2OJe+tE+gLg@mail.gmail.com>
Date:   Wed, 29 Apr 2020 08:40:03 +0200
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: don't call sleeping functions with a spinlock taken

wt., 28 kwi 2020 o 17:53 Andy Shevchenko <andy.shevchenko@...il.com> napisał(a):
>
> On Tue, Apr 14, 2020 at 6:35 PM Bartosz Golaszewski
> <bgolaszewski@...libre.com> wrote:
> >
> > wt., 14 kwi 2020 o 14:00 Linus Walleij <linus.walleij@...aro.org> napisał(a):
> > >
> > > On Fri, Mar 20, 2020 at 10:31 AM Bartosz Golaszewski <brgl@...ev.pl> wrote:
> > >
> > > > From: Bartosz Golaszewski <bgolaszewski@...libre.com>
> > > >
> > > > We must not call pinctrl_gpio_can_use_line() with the gpio_lock taken
> > > > as it takes a mutex internally. Let's move the call before taking the
> > > > spinlock and store the return value.
> > > >
> > > > This isn't perfect - there's a moment between calling
> > > > pinctrl_gpio_can_use_line() and taking the spinlock where the situation
> > > > can change but it isn't a regression either: previously this part wasn't
> > > > protected at all and it only affects the information user-space is
> > > > seeing.
>
> It seems I have no original at hand, so, commenting here.
>
> It looks like we need a mutex less function which can be used here and
> in the call you are considering racy.

The thing is this mutex is in pinctrl - we'd need to export it too so
that gpio can use it.

Bart