linux-kernel - Deadlock in grgpio_irq

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Date:	Sun,  2 Aug 2015 23:15:22 +0700
From:	Alexey Khoroshilov <khoroshilov@...ras.ru>
To:	Andreas Larsson <andreas@...sler.com>,
	Linus Walleij <linus.walleij@...aro.org>
Cc:	Alexey Khoroshilov <khoroshilov@...ras.ru>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
	ldv-project@...uxtesting.org
Subject: Deadlock in grgpio_irq_unmap()

Dear colleagus,

grgpio_irq_unmap() code looks quite suspicious regarding usage of
priv->bgc.lock spinlock.

It locks the spinlock in line 310:
        spin_lock_irqsave(&priv->bgc.lock, flags);
and then it can call grgpio_set_imask() in line 317:
        grgpio_set_imask(priv, i, 0);

But grgpio_set_imask() unconditionally locks the spinlock by itself.

static void grgpio_set_imask(struct grgpio_priv *priv, unsigned int offset,
			     int val)
{
	struct bgpio_chip *bgc = &priv->bgc;
	unsigned long mask = bgc->pin2mask(bgc, offset);
	unsigned long flags;

	spin_lock_irqsave(&bgc->lock, flags);

	if (val)
		priv->imask |= mask;
	else
		priv->imask &= ~mask;
	bgc->write_reg(priv->regs + GRGPIO_IMASK, priv->imask);

	spin_unlock_irqrestore(&bgc->lock, flags);
}

So, it looks like unavoidable deadlock here.

Found by Linux Driver Verification project (linuxtesting.org).

--
Alexey Khoroshilov
Linux Verification Center, ISPRAS
web: http://linuxtesting.org

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