linux-kernel - Re: [PATCH] mailbox: always wait in mbox_send

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Date:   Mon, 20 Mar 2017 18:47:14 +0000
From:   Alexey Klimov <alexey.klimov@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-kernel@...r.kernel.org,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Jassi Brar <jassisinghbrar@...il.com>
Subject: Re: [PATCH] mailbox: always wait in mbox_send_message for blocking
 tx mode

Hi Sudeep,

thanks for sending this patch.

On Mon, Mar 20, 2017 at 03:40:10PM +0000, Sudeep Holla wrote:
> There exists a race when msg_submit return immediately as there was an
> active request being processed which may have completed just before it's
> checked again in mbox_send_message. This will result in return to the
> caller without waiting in mbox_send_message even when it's blocking Tx.
> 
> This patch fixes the issue by making use of non-negative token returned
> by add_to_rbuf to check if the request was queued and block always if
> so in blocking Tx mode.
> 
> Fixes: 2b6d83e2b8b7 ("mailbox: Introduce framework for mailbox")
> Cc: Jassi Brar <jassisinghbrar@...il.com>
> Reported-by: Alexey Klimov <alexey.klimov@....com>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/mailbox/mailbox.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
> index 4671f8a12872..d5895791ab5d 100644
> --- a/drivers/mailbox/mailbox.c
> +++ b/drivers/mailbox/mailbox.c
> @@ -260,7 +260,7 @@ int mbox_send_message(struct mbox_chan *chan, void *mssg)
>  
>  	msg_submit(chan);
>  
> -	if (chan->cl->tx_block && chan->active_req) {
> +	if (chan->cl->tx_block && t >= 0) {

What do you think about removing t>=0 at all?
If add_to_rbuf() above returns negative number then we won't reach this point
in code at all and quit this function with error. If execution reaches this line then
we can say that t is definetely >= 0 and maybe it shouldn't be checked.


Best regards,
Alexey