linux-kernel - Re: [PATCH] pinctrl: baytrail: Use raw

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Date:	Wed, 26 Aug 2015 09:26:31 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: baytrail: Use raw_spinlock for locking

On Mon, Aug 17, 2015 at 3:03 PM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:

> The Intel Baytrail pinctrl driver implements irqchip callbacks which are
> called with desc->lock raw_spinlock held. In mainline this is fine because
> spinlock resolves to raw_spinlock. However, running the same code in -rt we
> get:
>
>  BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
>  in_atomic(): 1, irqs_disabled(): 1, pid: 0, name: swapper/0
>  Preemption disabled at:[<ffffffff81092e9f>] cpu_startup_entry+0x17f/0x480
>
>  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.1.5-rt5 #13
>   ...
>  Call Trace:
>   <IRQ>  [<ffffffff816283c6>] dump_stack+0x4a/0x61
>   [<ffffffff81077e17>] ___might_sleep+0xe7/0x170
>   [<ffffffff8162d6cf>] rt_spin_lock+0x1f/0x50
>   [<ffffffff812e3b88>] byt_gpio_clear_triggering+0x38/0x60
>   [<ffffffff812e3bc1>] byt_irq_mask+0x11/0x20
>   [<ffffffff810a7013>] handle_level_irq+0x83/0x150
>   [<ffffffff810a3457>] generic_handle_irq+0x27/0x40
>   [<ffffffff812e3a5f>] byt_gpio_irq_handler+0x7f/0xc0
>   [<ffffffff810050aa>] handle_irq+0xaa/0x190
>   ...
>
> This is because in -rt spinlocks are preemptible so taking the driver
> private spinlock in irqchip callbacks causes might_sleep() to trigger.
>
> In order to keep -rt happy but at the same time make sure that register
> accesses get serialized, convert the driver to use raw_spinlock instead.
>
> Also shorten the critical section a bit in few places.
>
> Suggested-by: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>

Awesome job Mika, patch applied.

Yours,
Linus Walleij
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