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Date:	Thu, 3 Jan 2013 20:27:01 -0200
From:	Gustavo Padovan <gustavo@...ovan.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Marcel Holtmann <marcel@...tmann.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH 12/25] bluetooth/l2cap: don't use [delayed_]work_pending()

Hi Tejun,

* Tejun Heo <tj@...nel.org> [2012-12-21 17:57:02 -0800]:

> There's no need to test whether a (delayed) work item in pending
> before queueing, flushing or cancelling it.  Most uses are unnecessary
> and quite a few of them are buggy.
> 
> Reimplement l2cap_set_timer() such that it uses mod_delayed_work() or
> schedule_delayed_work() depending on a new param @override and let the
> users specify whether to override or not instead of using
> delayed_work_pending().
> 
> Only compile tested.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Marcel Holtmann <marcel@...tmann.org>
> Cc: Gustavo Padovan <gustavo@...ovan.org>
> Cc: Johan Hedberg <johan.hedberg@...il.com>
> Cc: linux-bluetooth@...r.kernel.org
> ---
> Please let me know how this patch should be routed.  I can take it
> through the workqueue tree if necessary.
> 
> Thanks.
> 
>  include/net/bluetooth/l2cap.h | 24 ++++++++++++++++--------
>  net/bluetooth/l2cap_core.c    |  7 +++----
>  2 files changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h
> index 7588ef4..f12cbeb 100644
> --- a/include/net/bluetooth/l2cap.h
> +++ b/include/net/bluetooth/l2cap.h
> @@ -718,17 +718,25 @@ static inline void l2cap_chan_unlock(struct l2cap_chan *chan)
>  }
>  
>  static inline void l2cap_set_timer(struct l2cap_chan *chan,
> -				   struct delayed_work *work, long timeout)
> +				   struct delayed_work *work, long timeout,
> +				   bool override)
>  {
> +	bool was_pending;
> +
>  	BT_DBG("chan %p state %s timeout %ld", chan,
>  	       state_to_string(chan->state), timeout);
>  
> -	/* If delayed work cancelled do not hold(chan)
> -	   since it is already done with previous set_timer */
> -	if (!cancel_delayed_work(work))
> -		l2cap_chan_hold(chan);
> +	/* @work should hold a reference to @chan */
> +	l2cap_chan_hold(chan);
> +
> +	if (override)
> +		was_pending = mod_delayed_work(system_wq, work, timeout);
> +	else
> +		was_pending = !schedule_delayed_work(work, timeout);
>  
> -	schedule_delayed_work(work, timeout);
> +	/* if @work was already pending, lose the extra ref */
> +	if (was_pending)
> +		l2cap_chan_put(chan);
>  }
>  
>  static inline bool l2cap_clear_timer(struct l2cap_chan *chan,
> @@ -745,12 +753,12 @@ static inline bool l2cap_clear_timer(struct l2cap_chan *chan,
>  	return ret;
>  }
>  
> -#define __set_chan_timer(c, t) l2cap_set_timer(c, &c->chan_timer, (t))
> +#define __set_chan_timer(c, t) l2cap_set_timer(c, &c->chan_timer, (t), true)
>  #define __clear_chan_timer(c) l2cap_clear_timer(c, &c->chan_timer)
>  #define __clear_retrans_timer(c) l2cap_clear_timer(c, &c->retrans_timer)
>  #define __clear_monitor_timer(c) l2cap_clear_timer(c, &c->monitor_timer)
>  #define __set_ack_timer(c) l2cap_set_timer(c, &chan->ack_timer, \
> -		msecs_to_jiffies(L2CAP_DEFAULT_ACK_TO));
> +		msecs_to_jiffies(L2CAP_DEFAULT_ACK_TO), true);
>  #define __clear_ack_timer(c) l2cap_clear_timer(c, &c->ack_timer)
>  
>  static inline int __seq_offset(struct l2cap_chan *chan, __u16 seq1, __u16 seq2)
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 2c78208..91db91c 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -246,10 +246,9 @@ static inline void l2cap_chan_set_err(struct l2cap_chan *chan, int err)
>  
>  static void __set_retrans_timer(struct l2cap_chan *chan)
>  {
> -	if (!delayed_work_pending(&chan->monitor_timer) &&
> -	    chan->retrans_timeout) {
> +	if (chan->retrans_timeout) {
>  		l2cap_set_timer(chan, &chan->retrans_timer,
> -				msecs_to_jiffies(chan->retrans_timeout));
> +				msecs_to_jiffies(chan->retrans_timeout), false);

Did you notice we are talking about two different works here?
delayed_work_pending() is checking the monitor_timer while l2cap_set_timer is
setting the retrans_timer. We can't run one of them while the is running.
This mean you can just get rid of the override flag and simplify this patch a
lot.

	Gustavo
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