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From:   Chengfeng Ye <dg573847474@gmail.com>
To:     agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org,
        lee@kernel.org
Cc:     linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Chengfeng Ye <dg573847474@gmail.com>
Subject: [PATCH] mfd: qcom-pm8xxx: Fix potential deadlock on &chip->pm_irq_lock
Date:   Wed, 28 Jun 2023 07:28:40 +0000
Message-Id: <20230628072840.28587-1-dg573847474@gmail.com>
Precedence: bulk

As &chip->pm_irq_lock is acquired by pm8xxx_irq_handler() under irq
context, other process context code should disable irq before acquiring
the lock.

I think .irq_set_type and .irq_get_irqchip_state callbacks should be
executed from process context without irq disabled by default. Thus the
same lock acquision should disable irq.

Possible deadlock scenario
pm8xxx_irq_set_type()
    -> pm8xxx_config_irq()
    -> spin_lock(&chip->pm_irq_lock)
        <irq interrupt>
        -> pm8xxx_irq_handler()
        -> pm8xxx_irq_master_handler()
        -> pm8xxx_irq_block_handler()
        -> pm8xxx_read_block_irq()
        -> spin_lock(&chip->pm_irq_lock) (deadlock here)

This flaw was found using an experimental static analysis tool we are
developing for irq-related deadlock.

The tentative patch fix the potential deadlock by spin_lock_irqsave().

Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 drivers/mfd/qcom-pm8xxx.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/mfd/qcom-pm8xxx.c b/drivers/mfd/qcom-pm8xxx.c
index 9a948df8c28d..07c531bd1236 100644
--- a/drivers/mfd/qcom-pm8xxx.c
+++ b/drivers/mfd/qcom-pm8xxx.c
@@ -103,8 +103,9 @@ static int
 pm8xxx_config_irq(struct pm_irq_chip *chip, unsigned int bp, unsigned int cp)
 {
 	int	rc;
+	unsigned long flags;
 
-	spin_lock(&chip->pm_irq_lock);
+	spin_lock_irqsave(&chip->pm_irq_lock, flags);
 	rc = regmap_write(chip->regmap, SSBI_REG_ADDR_IRQ_BLK_SEL, bp);
 	if (rc) {
 		pr_err("Failed Selecting Block %d rc=%d\n", bp, rc);
@@ -116,7 +117,7 @@ pm8xxx_config_irq(struct pm_irq_chip *chip, unsigned int bp, unsigned int cp)
 	if (rc)
 		pr_err("Failed Configuring IRQ rc=%d\n", rc);
 bail:
-	spin_unlock(&chip->pm_irq_lock);
+	spin_unlock_irqrestore(&chip->pm_irq_lock, flags);
 	return rc;
 }
 
@@ -321,6 +322,7 @@ static int pm8xxx_irq_get_irqchip_state(struct irq_data *d,
 	struct pm_irq_chip *chip = irq_data_get_irq_chip_data(d);
 	unsigned int pmirq = irqd_to_hwirq(d);
 	unsigned int bits;
+	unsigned long flags;
 	int irq_bit;
 	u8 block;
 	int rc;
@@ -331,7 +333,7 @@ static int pm8xxx_irq_get_irqchip_state(struct irq_data *d,
 	block = pmirq / 8;
 	irq_bit = pmirq % 8;
 
-	spin_lock(&chip->pm_irq_lock);
+	spin_lock_irqsave(&chip->pm_irq_lock, flags);
 	rc = regmap_write(chip->regmap, SSBI_REG_ADDR_IRQ_BLK_SEL, block);
 	if (rc) {
 		pr_err("Failed Selecting Block %d rc=%d\n", block, rc);
@@ -346,7 +348,7 @@ static int pm8xxx_irq_get_irqchip_state(struct irq_data *d,
 
 	*state = !!(bits & BIT(irq_bit));
 bail:
-	spin_unlock(&chip->pm_irq_lock);
+	spin_unlock_irqrestore(&chip->pm_irq_lock, flags);
 
 	return rc;
 }
-- 
2.17.1