linux-kernel - [PATCH] iio: light: opt3001: fix deadlock due to concurrent flag access

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Message-Id: <20250321-opt3001-irq-fix-v1-1-6c520d851562@bootlin.com>
Date: Fri, 21 Mar 2025 19:10:00 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Jonathan Cameron <jic23@...nel.org>, 
 Lars-Peter Clausen <lars@...afoo.de>, Felipe Balbi <balbi@...com>
Cc: Andreas Dannenberg <dannenberg@...com>, David Frey <dpfrey@...il.com>, 
 Emil Gedenryd <emil.gedenryd@...s.com>, 
 Alexander Koch <mail@...xanderkoch.net>, Jiri Valek - 2N <valek@...cz>, 
 Hui Pu <Hui.Pu@...ealthcare.com>, 
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, linux-iio@...r.kernel.org, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Luca Ceresoli <luca.ceresoli@...tlin.com>
Subject: [PATCH] iio: light: opt3001: fix deadlock due to concurrent flag
 access

The threaded IRQ function in this driver is reading the flag twice: once to
lock a mutex and once to unlock it. Even though the code setting the flag
is designed to prevent it, there are subtle cases where the flag could be
true at the mutex_lock stage and false at the mutex_unlock stage. This
results in the mutex not being unlocked, resulting in a deadlock.

Fix it by making the opt3001_irq() code generally more robust, reading the
flag into a variable and using the variable value at both stages.

Fixes: 94a9b7b1809f ("iio: light: add support for TI's opt3001 light sensor")
Cc: stable@...r.kernel.org
Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
---
 drivers/iio/light/opt3001.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/light/opt3001.c b/drivers/iio/light/opt3001.c
index 65b295877b41588d40234ca7681bfee291e937c2..393a3d2fbe1d7320a243d3b6720e98b90f17baca 100644
--- a/drivers/iio/light/opt3001.c
+++ b/drivers/iio/light/opt3001.c
@@ -788,8 +788,9 @@ static irqreturn_t opt3001_irq(int irq, void *_iio)
 	int ret;
 	bool wake_result_ready_queue = false;
 	enum iio_chan_type chan_type = opt->chip_info->chan_type;
+	bool ok_to_ignore_lock = opt->ok_to_ignore_lock;
 
-	if (!opt->ok_to_ignore_lock)
+	if (!ok_to_ignore_lock)
 		mutex_lock(&opt->lock);
 
 	ret = i2c_smbus_read_word_swapped(opt->client, OPT3001_CONFIGURATION);
@@ -826,7 +827,7 @@ static irqreturn_t opt3001_irq(int irq, void *_iio)
 	}
 
 out:
-	if (!opt->ok_to_ignore_lock)
+	if (!ok_to_ignore_lock)
 		mutex_unlock(&opt->lock);
 
 	if (wake_result_ready_queue)

---
base-commit: 250a4b882cf37d9719874253f055aad211f2c317
change-id: 20250321-opt3001-irq-fix-f7eecd4e2e9c

Best regards,
-- 
Luca Ceresoli <luca.ceresoli@...tlin.com>