linux-kernel - Re: [PATCH 1/5] gpio: thunderx: avoid potential deadlock

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Date:   Tue, 31 May 2022 19:30:06 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Piyush Malgujar <pmalgujar@...vell.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Robert Richter <rric@...nel.org>, cchavva@...vell.com,
        wsadowski@...vell.com
Subject: Re: [PATCH 1/5] gpio: thunderx: avoid potential deadlock

On Wed, May 25, 2022 at 3:17 PM Piyush Malgujar <pmalgujar@...vell.com> wrote:
>
> On Mon, May 02, 2022 at 01:18:49PM +0200, Bartosz Golaszewski wrote:
> > On Wed, Apr 27, 2022 at 4:46 PM Piyush Malgujar <pmalgujar@...vell.com> wrote:
> > >
> > > Using irqsave/irqrestore locking variants to avoid any deadlock.
> > >
> >
> > I see you'll be resending this anyway so would you mind providing an
> > example of a deadlock that is possible with no-irqsave variants?
> > Thanks.
> >
> > Bart
> >
> Hi Bartosz,
>
> Thanks for the review.
>
> Please find below the issue scenario:
> In the case when HARDIRQ-safe -> HARDIRQ-unsafe lock order is detected
> and interrupt occurs, deadlock could occur.
>
> ========================================================
> WARNING: possible irq lock inversion dependency detected
> 5.18.0-rc6 #4 Not tainted
> --------------------------------------------------------
> swapper/3/0 just changed the state of lock:
> ffff000110904cd8 (lock_class){-...}-{2:2}, at: handle_fasteoi_ack_irq+0x2c/0x1b0
> but this lock took another, HARDIRQ-unsafe lock in the past:
>  (&txgpio->lock){+.+.}-{2:2}
>
>
> and interrupts could create inverse lock ordering between them.
>
>
> other info that might help us debug this:
>  Possible interrupt unsafe locking scenario:
>
>        CPU0                    CPU1
>        ----                    ----
>   lock(&txgpio->lock);
>                                local_irq_disable();
>                                lock(lock_class);
>                                lock(&txgpio->lock);
>   <Interrupt>
>     lock(lock_class);
>
>  *** DEADLOCK ***
>
> ==========================================================
>
> Thanks,
> Piyush
> > > Signed-off-by: Piyush Malgujar <pmalgujar@...vell.com>
> > > ---

Thanks. What I meant exactly was: resend it with that info in the
commit message.

Bart