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Message-ID: <20250331163642.2382651-1-alexander.sverdlin@siemens.com>
Date: Mon, 31 Mar 2025 18:36:40 +0200
From: "A. Sverdlin" <alexander.sverdlin@...mens.com>
To: linux-iio@...r.kernel.org
Cc: Alexander Sverdlin <alexander.sverdlin@...mens.com>,
Oleksij Rempel <o.rempel@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
William Breathitt Gray <wbg@...nel.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH] counter: interrupt-cnt: Protect enable/disable OPs with mutex
From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
Enable/disable seems to be racy on SMP, consider the following scenario:
CPU0 CPU1
interrupt_cnt_enable_write(true)
{
if (priv->enabled == enable)
return 0;
if (enable) {
priv->enabled = true;
interrupt_cnt_enable_write(false)
{
if (priv->enabled == enable)
return 0;
if (enable) {
priv->enabled = true;
enable_irq(priv->irq);
} else {
disable_irq(priv->irq)
priv->enabled = false;
}
enable_irq(priv->irq);
} else {
disable_irq(priv->irq);
priv->enabled = false;
}
The above would result in priv->enabled == false, but IRQ left enabled.
Protect both write (above race) and read (to propagate the value on SMP)
callbacks with a mutex.
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
---
drivers/counter/interrupt-cnt.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/counter/interrupt-cnt.c b/drivers/counter/interrupt-cnt.c
index 949598d51575a..d83848d0fe2af 100644
--- a/drivers/counter/interrupt-cnt.c
+++ b/drivers/counter/interrupt-cnt.c
@@ -3,12 +3,14 @@
* Copyright (c) 2021 Pengutronix, Oleksij Rempel <kernel@...gutronix.de>
*/
+#include <linux/cleanup.h>
#include <linux/counter.h>
#include <linux/gpio/consumer.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
+#include <linux/mutex.h>
#include <linux/platform_device.h>
#include <linux/types.h>
@@ -19,6 +21,7 @@ struct interrupt_cnt_priv {
struct gpio_desc *gpio;
int irq;
bool enabled;
+ struct mutex lock;
struct counter_signal signals;
struct counter_synapse synapses;
struct counter_count cnts;
@@ -41,6 +44,8 @@ static int interrupt_cnt_enable_read(struct counter_device *counter,
{
struct interrupt_cnt_priv *priv = counter_priv(counter);
+ guard(mutex)(&priv->lock);
+
*enable = priv->enabled;
return 0;
@@ -51,6 +56,8 @@ static int interrupt_cnt_enable_write(struct counter_device *counter,
{
struct interrupt_cnt_priv *priv = counter_priv(counter);
+ guard(mutex)(&priv->lock);
+
if (priv->enabled == enable)
return 0;
@@ -227,6 +234,8 @@ static int interrupt_cnt_probe(struct platform_device *pdev)
if (ret)
return ret;
+ mutex_init(&priv->lock);
+
ret = devm_counter_add(dev, counter);
if (ret < 0)
return dev_err_probe(dev, ret, "Failed to add counter\n");
--
2.49.0
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