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Message-ID: <CAKdAkRTxN3TrNYwFB1AXz4XgOoJdKpgkgHSdqf299CoHfMZ2vQ@mail.gmail.com>
Date: Mon, 13 Feb 2017 13:27:26 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Jeffy Chen <jeffy.chen@...k-chips.com>
Cc: linux-bluetooth@...r.kernel.org,
Brian Norris <briannorris@...omium.org>,
Douglas Anderson <dianders@...omium.org>,
Johan Hedberg <johan.hedberg@...el.com>,
Peter Hurley <peter@...leysoftware.com>,
Johan Hedberg <johan.hedberg@...il.com>,
netdev <netdev@...r.kernel.org>,
lkml <linux-kernel@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
Marcel Holtmann <marcel@...tmann.org>,
Gustavo Padovan <gustavo@...ovan.org>
Subject: Re: [PATCH v3 3/3] Bluetooth: hidp: fix possible might sleep error in hidp_session_thread
Hi Jeffy,
On Sun, Feb 12, 2017 at 8:12 PM, Jeffy Chen <jeffy.chen@...k-chips.com> wrote:
> It looks like hidp_session_thread 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@...k-chips.com>
> 1/ Fix could not wake up by wake attempts on original wait queues.
> 2/ Remove unnecessary memory barrier before wake_up_* functions.
>
> ---
>
> Changes in v3: None
> Changes in v2: None
>
> net/bluetooth/hidp/core.c | 33 ++++++++++++++++++++++-----------
> 1 file changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/net/bluetooth/hidp/core.c b/net/bluetooth/hidp/core.c
> index 0bec458..076bc50 100644
> --- a/net/bluetooth/hidp/core.c
> +++ b/net/bluetooth/hidp/core.c
> @@ -36,6 +36,7 @@
> #define VERSION "1.2"
>
> static DECLARE_RWSEM(hidp_session_sem);
> +static DECLARE_WAIT_QUEUE_HEAD(hidp_session_wq);
> static LIST_HEAD(hidp_session_list);
>
> static unsigned char hidp_keycode[256] = {
> @@ -1068,12 +1069,12 @@ static int hidp_session_start_sync(struct hidp_session *session)
> * Wake up session thread and notify it to stop. This is asynchronous and
> * returns immediately. Call this whenever a runtime error occurs and you want
> * the session to stop.
> - * Note: wake_up_process() performs any necessary memory-barriers for us.
> + * Note: wake_up_interruptible() performs any necessary memory-barriers for us.
> */
> static void hidp_session_terminate(struct hidp_session *session)
> {
> atomic_inc(&session->terminate);
> - wake_up_process(session->task);
> + wake_up_interruptible(&hidp_session_wq);
> }
>
> /*
> @@ -1180,7 +1181,9 @@ static void hidp_session_run(struct hidp_session *session)
> struct sock *ctrl_sk = session->ctrl_sock->sk;
> struct sock *intr_sk = session->intr_sock->sk;
> struct sk_buff *skb;
> + DEFINE_WAIT_FUNC(wait, woken_wake_function);
>
> + add_wait_queue(&hidp_session_wq, &wait);
> for (;;) {
> /*
> * This thread can be woken up two ways:
> @@ -1188,12 +1191,10 @@ static void hidp_session_run(struct hidp_session *session)
> * session->terminate flag and wakes this thread up.
> * - Via modifying the socket state of ctrl/intr_sock. This
> * thread is woken up by ->sk_state_changed().
> - *
> - * Note: set_current_state() performs any necessary
> - * memory-barriers for us.
> */
> - set_current_state(TASK_INTERRUPTIBLE);
>
> + /* Ensure session->terminate is updated */
> + smp_mb__before_atomic();
> if (atomic_read(&session->terminate))
> break;
>
> @@ -1227,11 +1228,22 @@ static void hidp_session_run(struct hidp_session *session)
> hidp_process_transmit(session, &session->ctrl_transmit,
> session->ctrl_sock);
>
> - schedule();
> + wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
> }
> + remove_wait_queue(&hidp_session_wq, &wait);
>
> atomic_inc(&session->terminate);
> - set_current_state(TASK_RUNNING);
> +
> + /* Ensure session->terminate is updated */
> + smp_mb__after_atomic();
> +}
> +
> +int hidp_session_wake_function(wait_queue_t *wait, unsigned int mode,
> + int sync, void *key)
static?
> +{
> + wake_up_interruptible(&hidp_session_wq);
> +
> + return default_wake_function(wait, mode, sync, key);
I do not think you need to call default_wake_function() here: the
process is waiting on hidp_session_wq, so the wakeup above is what
will wake up the session. By the time you get to call
default_wake_function() task will already be in wrong state. I think
we should simply return "false" instead of calling
default_wake_function().
> }
>
> /*
> @@ -1244,7 +1256,8 @@ static void hidp_session_run(struct hidp_session *session)
> static int hidp_session_thread(void *arg)
> {
> struct hidp_session *session = arg;
> - wait_queue_t ctrl_wait, intr_wait;
> + DEFINE_WAIT_FUNC(ctrl_wait, hidp_session_wake_function);
> + DEFINE_WAIT_FUNC(intr_wait, hidp_session_wake_function);
>
> BT_DBG("session %p", session);
>
> @@ -1254,8 +1267,6 @@ static int hidp_session_thread(void *arg)
> set_user_nice(current, -15);
> hidp_set_timer(session);
>
> - init_waitqueue_entry(&ctrl_wait, current);
> - init_waitqueue_entry(&intr_wait, current);
> add_wait_queue(sk_sleep(session->ctrl_sock->sk), &ctrl_wait);
> add_wait_queue(sk_sleep(session->intr_sock->sk), &intr_wait);
> /* This memory barrier is paired with wq_has_sleeper(). See
> --
> 2.1.4
>
>
Thanks.
--
Dmitry
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