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Message-ID: <64c77cc8-7327-d822-5976-c84b3d452ac5@arm.com>
Date: Wed, 29 Mar 2017 19:01:09 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Jassi Brar <jassisinghbrar@...il.com>, linux-kernel@...r.kernel.org
Cc: Sudeep Holla <sudeep.holla@....com>, alexey.klimov@....com,
Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH] mailbox: fix completion order for blocking requests
On 29/03/17 18:43, Jassi Brar wrote:
> Currently two threads, wait on blocking requests, could wake up for
> completion of request of each other as ...
>
> Thread#1(T1) Thread#2(T2)
> mbox_send_message mbox_send_message
> | |
> V |
> add_to_rbuf(M1) V
> | add_to_rbuf(M2)
> | |
> | V
> V msg_submit(picks M1)
> msg_submit |
> | V
> V wait_for_completion(on M2)
> wait_for_completion(on M1) | (1st in waitQ)
> | (2nd in waitQ) V
> V wake_up(on completion of M1)<--incorrect
>
> Fix this situaion by assigning completion structures to each queued
> request, so that the threads could wait on their own completions.
>
Alexey came up with exact similar solution. I didn't like:
1. the static array just bloats the structure with equal no. of
completion which may be useless for !TXDONE_BY_POLL
2. We have client drivers already doing something similar. I wanted
to fix/move those along with this fix. Or at-least see the feasibiliy
> Reported-by: Alexey Klimov <alexey.klimov@....com>
> Signed-off-by: Jassi Brar <jaswinder.singh@...aro.org>
> ---
> drivers/mailbox/mailbox.c | 15 +++++++++++----
> drivers/mailbox/omap-mailbox.c | 2 +-
> drivers/mailbox/pcc.c | 2 +-
> include/linux/mailbox_controller.h | 6 ++++--
> 4 files changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> index 9dfbf7e..e06c50c 100644
> --- a/drivers/mailbox/mailbox.c
> +++ b/drivers/mailbox/mailbox.c
> @@ -41,6 +41,7 @@ static int add_to_rbuf(struct mbox_chan *chan, void *mssg)
>
> idx = chan->msg_free;
> chan->msg_data[idx] = mssg;
> + init_completion(&chan->tx_cmpl[idx]);
reinit would be better.
> chan->msg_count++;
>
> if (idx == MBOX_TX_QUEUE_LEN - 1)
> @@ -73,6 +74,7 @@ static void msg_submit(struct mbox_chan *chan)
> idx += MBOX_TX_QUEUE_LEN - count;
>
> data = chan->msg_data[idx];
> + chan->tx_complete = &chan->tx_cmpl[idx];
>
> if (chan->cl->tx_prepare)
> chan->cl->tx_prepare(chan->cl, data);
> @@ -81,7 +83,8 @@ static void msg_submit(struct mbox_chan *chan)
> if (!err) {
> chan->active_req = data;
> chan->msg_count--;
> - }
> + } else
> + chan->tx_complete = NULL;
> exit:
> spin_unlock_irqrestore(&chan->lock, flags);
>
> @@ -92,12 +95,15 @@ static void msg_submit(struct mbox_chan *chan)
>
> static void tx_tick(struct mbox_chan *chan, int r)
> {
> + struct completion *tx_complete;
> unsigned long flags;
> void *mssg;
>
> spin_lock_irqsave(&chan->lock, flags);
> mssg = chan->active_req;
> + tx_complete = chan->tx_complete;
> chan->active_req = NULL;
> + chan->tx_complete = NULL;
> spin_unlock_irqrestore(&chan->lock, flags);
>
> /* Submit next message */
> @@ -111,7 +117,7 @@ static void tx_tick(struct mbox_chan *chan, int r)
> chan->cl->tx_done(chan->cl, mssg, r);
>
> if (r != -ETIME && chan->cl->tx_block)
> - complete(&chan->tx_complete);
> + complete(tx_complete);
> }
>
> static enum hrtimer_restart txdone_hrtimer(struct hrtimer *hrtimer)
> @@ -272,7 +278,7 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
> else
> wait = msecs_to_jiffies(chan->cl->tx_tout);
>
> - ret = wait_for_completion_timeout(&chan->tx_complete, wait);
> + ret = wait_for_completion_timeout(&chan->tx_cmpl[t], wait);
> if (ret == 0) {
> t = -ETIME;
> tx_tick(chan, t);
> @@ -348,7 +354,7 @@ struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index)
> chan->msg_count = 0;
> chan->active_req = NULL;
> chan->cl = cl;
> - init_completion(&chan->tx_complete);
> + chan->tx_complete = NULL;
>
> if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
> chan->txdone_method |= TXDONE_BY_ACK;
> @@ -414,6 +420,7 @@ void mbox_free_channel(struct mbox_chan *chan)
> spin_lock_irqsave(&chan->lock, flags);
> chan->cl = NULL;
> chan->active_req = NULL;
> + chan->tx_complete = NULL;
> if (chan->txdone_method == (TXDONE_BY_POLL | TXDONE_BY_ACK))
> chan->txdone_method = TXDONE_BY_POLL;
>
> diff --git a/drivers/mailbox/omap-mailbox.c b/drivers/mailbox/omap-mailbox.c
> index c5e8b9c..99b0841 100644
> --- a/drivers/mailbox/omap-mailbox.c
> +++ b/drivers/mailbox/omap-mailbox.c
> @@ -449,7 +449,7 @@ struct mbox_chan *omap_mbox_request_channel(struct mbox_client *cl,
> chan->msg_count = 0;
> chan->active_req = NULL;
> chan->cl = cl;
> - init_completion(&chan->tx_complete);
> + chan->tx_complete = NULL;
> spin_unlock_irqrestore(&chan->lock, flags);
>
> ret = chan->mbox->ops->startup(chan);
> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
> index dd9ecd35..b26cc9c 100644
> --- a/drivers/mailbox/pcc.c
> +++ b/drivers/mailbox/pcc.c
> @@ -263,7 +263,7 @@ struct mbox_chan *pcc_mbox_request_channel(struct mbox_client *cl,
> chan->msg_count = 0;
> chan->active_req = NULL;
> chan->cl = cl;
> - init_completion(&chan->tx_complete);
> + chan->tx_complete = NULL;
>
> if (chan->txdone_method == TXDONE_BY_POLL && cl->knows_txdone)
> chan->txdone_method |= TXDONE_BY_ACK;
> diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
> index 74deadb..aac8659 100644
> --- a/include/linux/mailbox_controller.h
> +++ b/include/linux/mailbox_controller.h
> @@ -106,11 +106,12 @@ struct mbox_controller {
> * @mbox: Pointer to the parent/provider of this channel
> * @txdone_method: Way to detect TXDone chosen by the API
> * @cl: Pointer to the current owner of this channel
> - * @tx_complete: Transmission completion
> + * @tx_complete: Pointer to current transmission completion
> * @active_req: Currently active request hook
> * @msg_count: No. of mssg currently queued
> * @msg_free: Index of next available mssg slot
> * @msg_data: Hook for data packet
> + * @tx_cmpl: Per-message completion structure
> * @lock: Serialise access to the channel
> * @con_priv: Hook for controller driver to attach private data
> */
> @@ -118,10 +119,11 @@ struct mbox_chan {
> struct mbox_controller *mbox;
> unsigned txdone_method;
> struct mbox_client *cl;
> - struct completion tx_complete;
> + struct completion *tx_complete;
> void *active_req;
> unsigned msg_count, msg_free;
> void *msg_data[MBOX_TX_QUEUE_LEN];
> + struct completion tx_cmpl[MBOX_TX_QUEUE_LEN];
May be better to encapsulate msg_data and tx_cmpl into structure so
that we just have one pointer to active_req and need not track
corresponding *tx_complete
--
Regards,
Sudeep
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