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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Tue, 19 Apr 2022 23:57:56 +0200
Message-ID: <CACRpkdYcCZ7zZkuVLMGnoqO69mJ5a-hEg2DV8PmzfwgBFzgVKQ@mail.gmail.com>
Subject: Re: [PATCH v3] gpio: use raw spinlock for gpio chip shadowed data
To:     Schspa Shi <schspa@gmail.com>
Cc:     brgl@bgdev.pl, andy.shevchenko@gmail.com, f.fainelli@gmail.com,
        fancer.lancer@gmail.com, hoan@os.amperecomputing.com,
        linux-arm-kernel@lists.infradead.org, linux-gpio@vger.kernel.org,
        linux-kernel@vger.kernel.org, opendmb@gmail.com
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On Tue, Apr 19, 2022 at 3:28 AM Schspa Shi <schspa@gmail.com> wrote:

> In case of PREEMPT_RT, there is a raw_spinlock -> spinlock dependency
> as the lockdep report shows.
>
> __irq_set_handler
>   irq_get_desc_buslock
>     __irq_get_desc_lock
>       raw_spin_lock_irqsave(&desc->lock, *flags);  // raw spinlock get here
>   __irq_do_set_handler
>     mask_ack_irq
>       dwapb_irq_ack
>         spin_lock_irqsave(&gc->bgpio_lock, flags); // sleep able spinlock
>   irq_put_desc_busunlock
>
> Replace with a raw lock to avoid BUGs. This lock is only used to access
> registers, and It's safe to replace with the raw lock without bad
> influence.
>
> [   15.090359][    T1] =============================
> [   15.090365][    T1] [ BUG: Invalid wait context ]
> [   15.090373][    T1] 5.10.59-rt52-00983-g186a6841c682-dirty #3 Not tainted
> [   15.090386][    T1] -----------------------------
> [   15.090392][    T1] swapper/0/1 is trying to lock:
> [   15.090402][    T1] 70ff00018507c188 (&gc->bgpio_lock){....}-{3:3}, at: _raw_spin_lock_irqsave+0x1c/0x28
> [   15.090470][    T1] other info that might help us debug this:
> [   15.090477][    T1] context-{5:5}
> [   15.090485][    T1] 3 locks held by swapper/0/1:
> [   15.090497][    T1]  #0: c2ff0001816de1a0 (&dev->mutex){....}-{4:4}, at: __device_driver_lock+0x98/0x104
> [   15.090553][    T1]  #1: ffff90001485b4b8 (irq_domain_mutex){+.+.}-{4:4}, at: irq_domain_associate+0xbc/0x6d4
> [   15.090606][    T1]  #2: 4bff000185d7a8e0 (lock_class){....}-{2:2}, at: _raw_spin_lock_irqsave+0x1c/0x28
> [   15.090654][    T1] stack backtrace:
> [   15.090661][    T1] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.10.59-rt52-00983-g186a6841c682-dirty #3
> [   15.090682][    T1] Hardware name: Horizon Robotics Journey 5 DVB (DT)
> [   15.090692][    T1] Call trace:
> ......
> [   15.090811][    T1]  _raw_spin_lock_irqsave+0x1c/0x28
> [   15.090828][    T1]  dwapb_irq_ack+0xb4/0x300
> [   15.090846][    T1]  __irq_do_set_handler+0x494/0xb2c
> [   15.090864][    T1]  __irq_set_handler+0x74/0x114
> [   15.090881][    T1]  irq_set_chip_and_handler_name+0x44/0x58
> [   15.090900][    T1]  gpiochip_irq_map+0x210/0x644
>
> Signed-off-by: Schspa Shi <schspa@gmail.com>

LGTM
Acked-by: Linus Walleij <linus.walleij@linaro.org>

Mostly hits drivers/gpio so this seems like something Bartosz
should merge.

Yours,
Linus Walleij