[PATCH] Bluetooth: btmrvl: fix thread stopping race

[PATCH] Bluetooth: btmrvl: fix thread stopping race

[Daniel Drake]

There is currently a race condition in the btmrvl_remove_card() which
is causing hangs on suspend for OLPC. When the race occurs,
kthread_stop() never returns.

The problem is that btmrvl_service_main_thread() calls kthread_should_stop()
and then does a fair number of things before restarting the loop and
sleeping.

If the thread gets stopped after kthread_should_stop() is checked, but
before the sleep happens, the thread will go to sleep and won't necessarily
be woken up.

Move the kthread_should_stop() check into a race-free place.

Signed-off-by: Daniel Drake <dsd@laptop.org>
---
 drivers/bluetooth/btmrvl_main.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/bluetooth/btmrvl_main.c b/drivers/bluetooth/btmrvl_main.c
index 3a4343b..9a9f518 100644
--- a/drivers/bluetooth/btmrvl_main.c
+++ b/drivers/bluetooth/btmrvl_main.c
@@ -498,6 +498,10 @@ static int btmrvl_service_main_thread(void *data)
 		add_wait_queue(&thread->wait_q, &wait);
 
 		set_current_state(TASK_INTERRUPTIBLE);
+		if (kthread_should_stop()) {
+			BT_DBG("main_thread: break from main thread");
+			break;
+		}
 
 		if (adapter->wakeup_tries ||
 				((!adapter->int_count) &&
@@ -513,11 +517,6 @@ static int btmrvl_service_main_thread(void *data)
 
 		BT_DBG("main_thread woke up");
 
-		if (kthread_should_stop()) {
-			BT_DBG("main_thread: break from main thread");
-			break;
-		}
-
 		spin_lock_irqsave(&priv->driver_lock, flags);
 		if (adapter->int_count) {
 			adapter->int_count = 0;
-- 
1.8.1.4

Re: [PATCH] Bluetooth: btmrvl: fix thread stopping race

[Gustavo Padovan]

Hi Daniel,

* Daniel Drake <dsd@laptop.org> [2013-06-11 15:40:20 -0400]:

> There is currently a race condition in the btmrvl_remove_card() which
> is causing hangs on suspend for OLPC. When the race occurs,
> kthread_stop() never returns.
> 
> The problem is that btmrvl_service_main_thread() calls kthread_should_stop()
> and then does a fair number of things before restarting the loop and
> sleeping.
> 
> If the thread gets stopped after kthread_should_stop() is checked, but
> before the sleep happens, the thread will go to sleep and won't necessarily
> be woken up.
> 
> Move the kthread_should_stop() check into a race-free place.
> 
> Signed-off-by: Daniel Drake <dsd@laptop.org>
> ---
>  drivers/bluetooth/btmrvl_main.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)

Patch has been applied to bluetooth.git. Thanks.

	Gustavo