[PATCH v4 2/3] Bluetooth: cmtp: fix possible might sleep error in cmtp_session

Jeffy Chen
2017-02-14T00:56:27Z

It looks like cmtp_session has same pattern as the issue reported in
old rfcomm:

while (1) {
set_current_state(TASK_INTERRUPTIBLE);
if (condition)
break;
// may call might_sleep here
schedule();
}
__set_current_state(TASK_RUNNING);

Which fixed at:
dfb2fae Bluetooth: Fix nested sleeps

So let's fix it at the same way, also follow the suggestion of:
https://lwn.net/Articles/628628/

Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Remove unnecessary memory barrier before wake_up_* functions.

---

Changes in v3:
Add brian's Reviewed-by.

Changes in v2: None

net/bluetooth/cmtp/core.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/net/bluetooth/cmtp/core.c b/net/bluetooth/cmtp/core.c
index 9e59b66..1152ce3 100644
--- a/net/bluetooth/cmtp/core.c
+++ b/net/bluetooth/cmtp/core.c
@@ -280,16 +280,16 @@ static int cmtp_session(void *arg)
struct cmtp_session *session = arg;
struct sock *sk = session->sock->sk;
struct sk_buff *skb;
- wait_queue_t wait;
+ DEFINE_WAIT_FUNC(wait, woken_wake_function);

BT_DBG("session %p", session);

set_user_nice(current, -15);

- init_waitqueue_entry(&wait, current);
add_wait_queue(sk_sleep(sk), &wait);
while (1) {
- set_current_state(TASK_INTERRUPTIBLE);
+ /* Ensure session->terminate is updated */
+ smp_mb__before_atomic();

if (atomic_read(&session->terminate))
break;
@@ -306,9 +306,8 @@ static int cmtp_session(void *arg)

cmtp_process_transmit(session);

- schedule();
+ wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
}
- __set_current_state(TASK_RUNNING);
remove_wait_queue(sk_sleep(sk), &wait);

down_write(&cmtp_session_sem);
@@ -393,7 +392,7 @@ int cmtp_add_connection(struct cmtp_connadd_req *req, struct socket *sock)
err = cmtp_attach_device(session);
if (err < 0) {
atomic_inc(&session->terminate);
- wake_up_process(session->task);
+ wake_up_interruptible(sk_sleep(session->sock->sk));
up_write(&cmtp_session_sem);
return err;
}
@@ -431,7 +430,11 @@ int cmtp_del_connection(struct cmtp_conndel_req *req)

/* Stop session thread */
atomic_inc(&session->terminate);
- wake_up_process(session->task);
+
+ /* Ensure session->terminate is updated */
+ smp_mb__after_atomic();
+
+ wake_up_interruptible(sk_sleep(session->sock->sk));
} else
err = -ENOENT;

--
2.1.4