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Date: Tue, 14 Feb 2017 08:57:50 +0800
From: jeffy <jeffy.chen@...k-chips.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.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 Dmitry,
On 02/14/2017 05:27 AM, Dmitry Torokhov wrote:
> 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?
Oops, sure.
>
>> +{
>> + 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().
Ok, thanx.
>
>> }
>>
>> /*
>> @@ -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.
>
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