Bluetooth: Fix hidp disconnect deadlocks and lost wakeup

Partial revert of commit aabf6f89. When the hidp session thread
was converted from kernel_thread to kthread, the atomic/wakeups
were replaced with kthread_stop. kthread_stop has blocking semantics
which are inappropriate for the hidp session kthread. In addition,
the kthread signals itself to terminate in hidp_process_hid_control()
- it cannot do this with kthread_stop().

Lastly, a wakeup can be lost if the wakeup happens between checking
for the loop exit condition and setting the current state to
TASK_INTERRUPTIBLE. (Without appropriate synchronization mechanisms,
the task state should not be changed between the condition test and
the yield - via schedule() - as this creates a race between the
wakeup and resetting the state back to interruptible.)

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

2 files changed, 12 insertions, 7 deletions

diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
index c405a954a603..43b4c2deb7cc 100644
--- a/net/bluetooth/hidp/core.c
+++ b/net/bluetooth/hidp/core.c
@@ -464,7 +464,8 @@ static void hidp_idle_timeout(unsigned long arg)
 {
         struct hidp_session *session = (struct hidp_session *) arg;
 
-        kthread_stop(session->task);
+        atomic_inc(&session->terminate);
+        wake_up_process(session->task);
 }
 
 static void hidp_set_timer(struct hidp_session *session)
@@ -535,7 +536,8 @@ static void hidp_process_hid_control(struct hidp_session *session,
                 skb_queue_purge(&session->ctrl_transmit);
                 skb_queue_purge(&session->intr_transmit);
 
-                kthread_stop(session->task);
+                atomic_inc(&session->terminate);
+                wake_up_process(current);
         }
 }
 
@@ -706,9 +708,8 @@ static int hidp_session(void *arg)
         add_wait_queue(sk_sleep(intr_sk), &intr_wait);
         session->waiting_for_startup = 0;
         wake_up_interruptible(&session->startup_queue);
-        while (!kthread_should_stop()) {
-                set_current_state(TASK_INTERRUPTIBLE);
-
+        set_current_state(TASK_INTERRUPTIBLE);
+        while (!atomic_read(&session->terminate)) {
                 if (ctrl_sk->sk_state != BT_CONNECTED ||
                                 intr_sk->sk_state != BT_CONNECTED)
                         break;
@@ -726,6 +727,7 @@ static int hidp_session(void *arg)
                 hidp_process_transmit(session);
 
                 schedule();
+                set_current_state(TASK_INTERRUPTIBLE);
         }
         set_current_state(TASK_RUNNING);
         remove_wait_queue(sk_sleep(intr_sk), &intr_wait);
@@ -1060,7 +1062,8 @@ int hidp_add_connection(struct hidp_connadd_req *req, struct socket *ctrl_sock,
 err_add_device:
         hid_destroy_device(session->hid);
         session->hid = NULL;
-        kthread_stop(session->task);
+        atomic_inc(&session->terminate);
+        wake_up_process(session->task);
 
 unlink:
         hidp_del_timer(session);
@@ -1111,7 +1114,8 @@ int hidp_del_connection(struct hidp_conndel_req *req)
                         skb_queue_purge(&session->ctrl_transmit);
                         skb_queue_purge(&session->intr_transmit);
 
-                        kthread_stop(session->task);
+                        atomic_inc(&session->terminate);
+                        wake_up_process(session->task);
                 }
         } else
                 err = -ENOENT;
diff --git a/net/bluetooth/hidp/hidp.h b/net/bluetooth/hidp/hidp.h
index 19e95004b286..af1bcc823f26 100644
--- a/net/bluetooth/hidp/hidp.h
+++ b/net/bluetooth/hidp/hidp.h
@@ -142,6 +142,7 @@ struct hidp_session {
         uint ctrl_mtu;
         uint intr_mtu;
 
+        atomic_t terminate;
         struct task_struct *task;
 
         unsigned char keys[8];