linux-kernel - [PATCH v3] HID: Replace semaphore driver

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Date:   Wed, 14 Jun 2017 11:42:20 +0530
From:   Binoy Jayan <binoy.jayan@...aro.org>
To:     Binoy Jayan <binoy.jayan@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Rajendra <rnayak@...eaurora.org>,
        Mark Brown <broonie@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        David Herrmann <dh.herrmann@...glemail.com>,
        Andrew de los Reyes <adlr@...omium.org>
Subject: [PATCH v3] HID: Replace semaphore driver_lock with mutex

The semaphore 'driver_lock' is used as a simple mutex, and
also unnecessary as suggested by Arnd. Hence removing it, as
the concurrency between the probe and remove is already
handled in the driver core.

Suggested-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Binoy Jayan <binoy.jayan@...aro.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
Reviewed-by: David Herrmann <dh.herrmann@...il.com>
---

v2 --> v3:
Removed reference to driver_lock in comments

v1 --> v2:
Removed driver_lock

 drivers/hid/hid-core.c | 15 ++++-----------
 include/linux/hid.h    |  3 +--
 2 files changed, 5 insertions(+), 13 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 04cee65..559533b 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -2225,11 +2225,9 @@ static int hid_device_probe(struct device *dev)
 	const struct hid_device_id *id;
 	int ret = 0;
 
-	if (down_interruptible(&hdev->driver_lock))
-		return -EINTR;
 	if (down_interruptible(&hdev->driver_input_lock)) {
 		ret = -EINTR;
-		goto unlock_driver_lock;
+		goto end;
 	}
 	hdev->io_started = false;
 
@@ -2256,8 +2254,7 @@ static int hid_device_probe(struct device *dev)
 unlock:
 	if (!hdev->io_started)
 		up(&hdev->driver_input_lock);
-unlock_driver_lock:
-	up(&hdev->driver_lock);
+end:
 	return ret;
 }
 
@@ -2267,11 +2264,9 @@ static int hid_device_remove(struct device *dev)
 	struct hid_driver *hdrv;
 	int ret = 0;
 
-	if (down_interruptible(&hdev->driver_lock))
-		return -EINTR;
 	if (down_interruptible(&hdev->driver_input_lock)) {
 		ret = -EINTR;
-		goto unlock_driver_lock;
+		goto end;
 	}
 	hdev->io_started = false;
 
@@ -2287,8 +2282,7 @@ static int hid_device_remove(struct device *dev)
 
 	if (!hdev->io_started)
 		up(&hdev->driver_input_lock);
-unlock_driver_lock:
-	up(&hdev->driver_lock);
+end:
 	return ret;
 }
 
@@ -2745,7 +2739,6 @@ struct hid_device *hid_allocate_device(void)
 	init_waitqueue_head(&hdev->debug_wait);
 	INIT_LIST_HEAD(&hdev->debug_list);
 	spin_lock_init(&hdev->debug_list_lock);
-	sema_init(&hdev->driver_lock, 1);
 	sema_init(&hdev->driver_input_lock, 1);
 
 	return hdev;
diff --git a/include/linux/hid.h b/include/linux/hid.h
index 5be325d..a49203f 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -516,7 +516,6 @@ struct hid_device {							/* device report descriptor */
 	struct hid_report_enum report_enum[HID_REPORT_TYPES];
 	struct work_struct led_work;					/* delayed LED worker */
 
-	struct semaphore driver_lock;					/* protects the current driver, except during input */
 	struct semaphore driver_input_lock;				/* protects the current driver */
 	struct device dev;						/* device */
 	struct hid_driver *driver;
@@ -538,7 +537,7 @@ struct hid_device {							/* device report descriptor */
 	unsigned int status;						/* see STAT flags above */
 	unsigned claimed;						/* Claimed by hidinput, hiddev? */
 	unsigned quirks;						/* Various quirks the device can pull on us */
-	bool io_started;						/* Protected by driver_lock. If IO has started */
+	bool io_started;						/* If IO has started */
 
 	struct list_head inputs;					/* The list of inputs */
 	void *hiddev;							/* The hiddev structure */
-- 
Binoy Jayan