[PATCH] platform/x86: quickstart: Fix race condition when reporting input event

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Since commit e2ffcda16290 ("ACPI: OSL: Allow Notify () handlers to run
on all CPUs"), the ACPI core allows multiple notify calls to be active
at the same time. This means that two instances of quickstart_notify()
running at the same time can mess which each others input sequences.

Fix this by protecting the input sequence with a mutex.

Compile-tested only.

Fixes: afd66f2a739e ("platform/x86: Add ACPI quickstart button (PNP0C32) driver")
Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
This applies on the branch "review-hans". Maybe we could somehow
document the concurrency rules for ACPI notify handlers?
 drivers/platform/x86/quickstart.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/platform/x86/quickstart.c b/drivers/platform/x86/quickstart.c
index ba3a7a25dda7..e40f852d42c1 100644
--- a/drivers/platform/x86/quickstart.c
+++ b/drivers/platform/x86/quickstart.c
@@ -18,6 +18,7 @@
 #include <linux/input/sparse-keymap.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
@@ -35,6 +36,7 @@

 struct quickstart_data {
 	struct device *dev;
+	struct mutex input_lock;	/* Protects input sequence during notify */
 	struct input_dev *input_device;
 	char input_name[32];
 	char phys[32];
@@ -73,7 +75,10 @@ static void quickstart_notify(acpi_handle handle, u32 event, void *context)

 	switch (event) {
+		mutex_lock(&data->input_lock);
 		sparse_keymap_report_event(data->input_device, 0x1, 1, true);
+		mutex_unlock(&data->input_lock);
 		acpi_bus_generate_netlink_event(DRIVER_NAME, dev_name(data->dev), event, 0);
@@ -147,6 +152,13 @@ static void quickstart_notify_remove(void *context)
 	acpi_remove_notify_handler(handle, ACPI_DEVICE_NOTIFY, quickstart_notify);

+static void quickstart_mutex_destroy(void *data)
+	struct mutex *lock = data;
+	mutex_destroy(lock);
 static int quickstart_probe(struct platform_device *pdev)
 	struct quickstart_data *data;
@@ -165,6 +177,11 @@ static int quickstart_probe(struct platform_device *pdev)
 	data->dev = &pdev->dev;
 	dev_set_drvdata(&pdev->dev, data);

+	mutex_init(&data->input_lock);
+	ret = devm_add_action_or_reset(&pdev->dev, quickstart_mutex_destroy, &data->input_lock);
+	if (ret < 0)
+		return ret;
 	/* We have to initialize the device wakeup before evaluating GHID because
 	 * doing so will notify the device if the button was used to wake the machine
 	 * from S5.

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