Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
MIME-Version: 1.0
References: <20220427144620.9105-1-pmalgujar@marvell.com> <20220427144620.9105-2-pmalgujar@marvell.com>
 <CAMRc=Mf91eMF7D6CRtA8-HQ7pdtP343WUGhLG4qti_9zJF4ELQ@mail.gmail.com> <20220525131738.GA10532@Dell2s-9>
In-Reply-To: <20220525131738.GA10532@Dell2s-9>
From:   Bartosz Golaszewski <brgl@bgdev.pl>
Date:   Tue, 31 May 2022 19:30:06 +0200
Message-ID: <CAMRc=Mds_cKkdDJUV5h7prfPg-rBms33uFad_S-zzPaws=qfLg@mail.gmail.com>
Subject: Re: [PATCH 1/5] gpio: thunderx: avoid potential deadlock
To:     Piyush Malgujar <pmalgujar@marvell.com>
Cc:     "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        devicetree <devicetree@vger.kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Robert Richter <rric@kernel.org>, cchavva@marvell.com,
        wsadowski@marvell.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, May 25, 2022 at 3:17 PM Piyush Malgujar <pmalgujar@marvell.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@marvell.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@marvell.com>
> > > ---

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

Bart