[PATCH 5.15.y] media: rc: Fix ABBA deadlock by making locks more fine grained

[Sasha Levin <sashal@kernel.org>]

From: Sean Young <sean@mess.org>

[ Upstream commit c6d68866ad8aa1e957a3e5a6ede971148f1e3d59 ]

The ir_raw_event_unregister() function takes the ir_raw_handler_lock
first and then the rc_dev->lock. Other functions like change_protocol
do this in the reverse order.

This means that an ir decoder module unload and writing to the protocol
sysfs file can cause a deadlock.

ir_raw_handler_lock protects the client list, amongst other things.
Split this out into a separate lock so we can ensure the locking
order is always the same.

Fixes: 93cffffc18f6 ("[media] media: rc: fix decoder module unloading")
Signed-off-by: Sean Young <sean@mess.org>
Cc: stable@vger.kernel.org
Acked-by: Hans Verkuil <hverkuil+cisco@kernel.org>
[ sashal: adjusted ir_raw_event_unregister() context for del_timer_sync() and the existing teardown sequence ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/media/rc/rc-ir-raw.c | 38 +++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/drivers/media/rc/rc-ir-raw.c b/drivers/media/rc/rc-ir-raw.c
index c65bba4ec4739..304cc47e781ed 100644
--- a/drivers/media/rc/rc-ir-raw.c
+++ b/drivers/media/rc/rc-ir-raw.c
@@ -10,7 +10,8 @@
 #include <linux/sched.h>
 #include "rc-core-priv.h"
 
-/* Used to keep track of IR raw clients, protected by ir_raw_handler_lock */
+/* Used to keep track of IR raw clients, protected by ir_raw_client_lock */
+static DEFINE_MUTEX(ir_raw_client_lock);
 static LIST_HEAD(ir_raw_client_list);
 
 /* Used to handle IR raw handler extensions */
@@ -290,13 +291,6 @@ static int change_protocol(struct rc_dev *dev, u64 *rc_proto)
 	return 0;
 }
 
-static void ir_raw_disable_protocols(struct rc_dev *dev, u64 protocols)
-{
-	mutex_lock(&dev->lock);
-	dev->enabled_protocols &= ~protocols;
-	mutex_unlock(&dev->lock);
-}
-
 /**
  * ir_raw_gen_manchester() - Encode data with Manchester (bi-phase) modulation.
  * @ev:		Pointer to pointer to next free event. *@ev is incremented for
@@ -634,15 +628,18 @@ int ir_raw_event_register(struct rc_dev *dev)
 {
 	struct task_struct *thread;
 
+	/* Holding dev->lock could result in a dead-lock */
+	lockdep_assert_not_held(&dev->lock);
+
 	thread = kthread_run(ir_raw_event_thread, dev->raw, "rc%u", dev->minor);
 	if (IS_ERR(thread))
 		return PTR_ERR(thread);
 
 	dev->raw->thread = thread;
 
-	mutex_lock(&ir_raw_handler_lock);
+	mutex_lock(&ir_raw_client_lock);
 	list_add_tail(&dev->raw->list, &ir_raw_client_list);
-	mutex_unlock(&ir_raw_handler_lock);
+	mutex_unlock(&ir_raw_client_lock);
 
 	return 0;
 }
@@ -666,8 +663,10 @@ void ir_raw_event_unregister(struct rc_dev *dev)
 	kthread_stop(dev->raw->thread);
 	del_timer_sync(&dev->raw->edge_handle);
 
-	mutex_lock(&ir_raw_handler_lock);
+	mutex_lock(&ir_raw_client_lock);
 	list_del(&dev->raw->list);
+
+	mutex_lock(&ir_raw_handler_lock);
 	list_for_each_entry(handler, &ir_raw_handler_list, list)
 		if (handler->raw_unregister &&
 		    (handler->protocols & dev->enabled_protocols))
@@ -683,6 +682,8 @@ void ir_raw_event_unregister(struct rc_dev *dev)
 	 * "device gone" is checked.
 	 */
 	mutex_unlock(&ir_raw_handler_lock);
+
+	mutex_unlock(&ir_raw_client_lock);
 }
 
 /*
@@ -705,15 +706,24 @@ void ir_raw_handler_unregister(struct ir_raw_handler *ir_raw_handler)
 	struct ir_raw_event_ctrl *raw;
 	u64 protocols = ir_raw_handler->protocols;
 
+	mutex_lock(&ir_raw_client_lock);
+
 	mutex_lock(&ir_raw_handler_lock);
 	list_del(&ir_raw_handler->list);
+	atomic64_andnot(protocols, &available_protocols);
+	mutex_unlock(&ir_raw_handler_lock);
+
 	list_for_each_entry(raw, &ir_raw_client_list, list) {
+		mutex_lock(&raw->dev->lock);
+		mutex_lock(&ir_raw_handler_lock);
 		if (ir_raw_handler->raw_unregister &&
 		    (raw->dev->enabled_protocols & protocols))
 			ir_raw_handler->raw_unregister(raw->dev);
-		ir_raw_disable_protocols(raw->dev, protocols);
+		raw->dev->enabled_protocols &= ~protocols;
+		mutex_unlock(&ir_raw_handler_lock);
+		mutex_unlock(&raw->dev->lock);
 	}
-	atomic64_andnot(protocols, &available_protocols);
-	mutex_unlock(&ir_raw_handler_lock);
+
+	mutex_unlock(&ir_raw_client_lock);
 }
 EXPORT_SYMBOL(ir_raw_handler_unregister);
-- 
2.53.0