linux-kernel - [PATCH AUTOSEL 5.12 066/160] pinctrl: mcp23s08: fix race condition in irq handler

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Date:   Tue,  6 Jul 2021 07:16:52 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Radim Pavlik <radim.pavlik@...-biometrics.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sasha Levin <sashal@...nel.org>, linux-gpio@...r.kernel.org
Subject: [PATCH AUTOSEL 5.12 066/160] pinctrl: mcp23s08: fix race condition in irq handler

From: Radim Pavlik <radim.pavlik@...-biometrics.com>

[ Upstream commit 897120d41e7afd9da435cb00041a142aeeb53c07 ]

Checking value of MCP_INTF in mcp23s08_irq suggests that the handler may be
called even when there is no interrupt pending.

But the actual interrupt could happened between reading MCP_INTF and MCP_GPIO.
In this situation we got nothing from MCP_INTF, but the event gets acknowledged
on the expander by reading MCP_GPIO. This leads to losing events.

Fix the problem by not reading any register until we see something in MCP_INTF.

The error was reproduced and fix tested on MCP23017.

Signed-off-by: Radim Pavlik <radim.pavlik@...-biometrics.com>
Link: https://lore.kernel.org/r/AM7PR06MB6769E1183F68DEBB252F665ABA3E9@AM7PR06MB6769.eurprd06.prod.outlook.com
Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/pinctrl/pinctrl-mcp23s08.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/pinctrl/pinctrl-mcp23s08.c b/drivers/pinctrl/pinctrl-mcp23s08.c
index ce2d8014b7e0..799d596a1a4b 100644
--- a/drivers/pinctrl/pinctrl-mcp23s08.c
+++ b/drivers/pinctrl/pinctrl-mcp23s08.c
@@ -351,6 +351,11 @@ static irqreturn_t mcp23s08_irq(int irq, void *data)
 	if (mcp_read(mcp, MCP_INTF, &intf))
 		goto unlock;
 
+	if (intf == 0) {
+		/* There is no interrupt pending */
+		return IRQ_HANDLED;
+	}
+
 	if (mcp_read(mcp, MCP_INTCAP, &intcap))
 		goto unlock;
 
@@ -368,11 +373,6 @@ static irqreturn_t mcp23s08_irq(int irq, void *data)
 	mcp->cached_gpio = gpio;
 	mutex_unlock(&mcp->lock);
 
-	if (intf == 0) {
-		/* There is no interrupt pending */
-		return IRQ_HANDLED;
-	}
-
 	dev_dbg(mcp->chip.parent,
 		"intcap 0x%04X intf 0x%04X gpio_orig 0x%04X gpio 0x%04X\n",
 		intcap, intf, gpio_orig, gpio);
-- 
2.30.2