gpio: eic-sprd: use raw_spinlock_t in the irq startup path

sprd_eic_irq_unmask() enables the GPIO IRQ and then updates controller
state through sprd_eic_update(), which takes sprd_eic->lock with
spin_lock_irqsave().  The callback can be reached from irq_startup()
while setting up a requested IRQ.  That path is not sleepable, but on
PREEMPT_RT a regular spinlock_t becomes a sleeping lock.

This issue was found by our static analysis tool and then manually
reviewed against the current tree.

The grounded PoC kept the request_threaded_irq() -> __setup_irq() ->
irq_startup() -> sprd_eic_irq_unmask() -> sprd_eic_update() carrier and
used the original spin_lock_irqsave(&sprd_eic->lock) edge.  Lockdep
reported:

  BUG: sleeping function called from invalid context
  hardirqs last disabled at ... __setup_irq.constprop.0 ... [vuln_msv]
  sprd_rt_spin_lock_irqsave+0x1c/0x30 [vuln_msv]
  sprd_eic_update.constprop.0+0x48/0x90 [vuln_msv]
  sprd_eic_irq_unmask.constprop.0+0x35/0x50 [vuln_msv]
  __setup_irq.constprop.0+0xd/0x30 [vuln_msv]

Convert the Spreadtrum EIC controller lock to raw_spinlock_t.  The
locked section only serializes MMIO register updates and does not contain
sleepable operations, so keeping it non-sleeping is appropriate for the
irqchip callbacks.

Fixes: 25518e024e ("gpio: Add Spreadtrum EIC driver support")
Cc: [email protected]
Signed-off-by: Runyu Xiao <[email protected]>
Reviewed-by: Sebastian Andrzej Siewior <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Bartosz Golaszewski <[email protected]>

drivers/gpio/gpio-eic-sprd.c

@@ -95,7 +95,7 @@ struct sprd_eic {
 	struct notifier_block irq_nb;
 	void __iomem *base[SPRD_EIC_MAX_BANK];
 	enum sprd_eic_type type;
-	spinlock_t lock;
+	raw_spinlock_t lock;
 	int irq;
 };
 
@@ -149,7 +149,7 @@ static void sprd_eic_update(struct gpio_chip *chip, unsigned int offset,
 	unsigned long flags;
 	u32 tmp;
 
-	spin_lock_irqsave(&sprd_eic->lock, flags);
+	raw_spin_lock_irqsave(&sprd_eic->lock, flags);
 	tmp = readl_relaxed(base + reg);
 
 	if (val)
@@ -158,7 +158,7 @@ static void sprd_eic_update(struct gpio_chip *chip, unsigned int offset,
 		tmp &= ~BIT(SPRD_EIC_BIT(offset));
 
 	writel_relaxed(tmp, base + reg);
-	spin_unlock_irqrestore(&sprd_eic->lock, flags);
+	raw_spin_unlock_irqrestore(&sprd_eic->lock, flags);
 }
 
 static int sprd_eic_read(struct gpio_chip *chip, unsigned int offset, u16 reg)
@@ -628,7 +628,7 @@ static int sprd_eic_probe(struct platform_device *pdev)
 	if (!sprd_eic)
 		return -ENOMEM;
 
-	spin_lock_init(&sprd_eic->lock);
+	raw_spin_lock_init(&sprd_eic->lock);
 	sprd_eic->type = pdata->type;
 
 	sprd_eic->irq = platform_get_irq(pdev, 0);