Re: [PATCH/RFC] serial: sh-sci: Fix exclusion of work_fn_rx and sci_dma_rx_complete

[Yoshihiro Kaneko <ykaneko0929@gmail.com>]

Hi Geert-san,

2015-07-15 21:53 GMT+09:00 Geert Uytterhoeven <geert@linux-m68k.org>:
> Hi Kaneko-san, Mizuguchi-san,
>
> On Sun, Jun 14, 2015 at 7:27 PM, Yoshihiro Kaneko <ykaneko0929@gmail.com> wrote:
>> From: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
>>
>> There is a problem when the sci_dma_rx_complete() is processed
>> before cancel process of work_fn_rx() completes by rx_timer_fn().
>> This patch locks work_fn_rx().
>>
>> Signed-off-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
>> Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
>
> Thanks for your patch!
>
> Unfortunately this is not sufficient. work_fn_rx() may race with
> sci_rx_dma_release(), too.

Thanks for your review!
Your following patch fixes that problem, right?
[PATCH/RFC v2 23/29] serial: sh-sci: Fix race condition between RX
work_struct and cleanup

Thanks,
Kaneko

>
>> ---
>>
>> This patch is based on the tty-next branch of Greg Kroah-Hartman's tty
>> tree.
>>
>>  drivers/tty/serial/sh-sci.c | 13 +++++++------
>>  1 file changed, 7 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
>> index b74a644..ef59842 100644
>> --- a/drivers/tty/serial/sh-sci.c
>> +++ b/drivers/tty/serial/sh-sci.c
>> @@ -1423,14 +1423,16 @@ static void work_fn_rx(struct work_struct *work)
>>         struct uart_port *port = &s->port;
>>         struct dma_async_tx_descriptor *desc;
>>         int new;
>> +       unsigned long flags;
>>
>> +       spin_lock_irqsave(&port->lock, flags);
>>         if (s->active_rx = s->cookie_rx[0]) {
>>                 new = 0;
>>         } else if (s->active_rx = s->cookie_rx[1]) {
>>                 new = 1;
>>         } else {
>>                 dev_err(port->dev, "cookie %d not found!\n", s->active_rx);
>> -               return;
>> +               goto out;
>>         }
>>         desc = s->desc_rx[new];
>>
>> @@ -1440,36 +1442,35 @@ static void work_fn_rx(struct work_struct *work)
>>                 struct dma_chan *chan = s->chan_rx;
>>                 struct shdma_desc *sh_desc = container_of(desc,
>>                                         struct shdma_desc, async_tx);
>> -               unsigned long flags;
>>                 int count;
>>
>>                 dmaengine_terminate_all(chan);
>>                 dev_dbg(port->dev, "Read %zu bytes with cookie %d\n",
>>                         sh_desc->partial, sh_desc->cookie);
>>
>> -               spin_lock_irqsave(&port->lock, flags);
>>                 count = sci_dma_rx_push(s, sh_desc->partial);
>> -               spin_unlock_irqrestore(&port->lock, flags);
>>
>>                 if (count)
>>                         tty_flip_buffer_push(&port->state->port);
>>
>>                 sci_submit_rx(s);
>>
>> -               return;
>> +               goto out;
>>         }
>>
>>         s->cookie_rx[new] = desc->tx_submit(desc);
>>         if (s->cookie_rx[new] < 0) {
>>                 dev_warn(port->dev, "Failed submitting Rx DMA descriptor\n");
>>                 sci_rx_dma_release(s, true);
>> -               return;
>> +               goto out;
>>         }
>>
>>         s->active_rx = s->cookie_rx[!new];
>>
>>         dev_dbg(port->dev, "%s: cookie %d #%d, new active #%d\n",
>>                 __func__, s->cookie_rx[new], new, s->active_rx);
>> +out:
>> +       spin_unlock_irqrestore(&port->lock, flags);
>>  }
>>
>>  static void work_fn_tx(struct work_struct *work)
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds