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SubjectRe: [PATCH] ipoctal: protect only the real critical section
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On Thu, 2014-06-26 at 09:46 +0200, Federico Vaga wrote:
> In some conditions (echo or particular sequence of special
> characters), on buffer push, the tty layer calls the write operation
> while we are holding the spinlock. This means deadlock within the same
> process on kernels version < 3.12. It seems not a problem on recent
> kernel, but the patch still valid as locking optimization.
>
> The protected variables by the spinlock are: xmit_buf, nb_bytes,
> pointer_read and pointer_write. So, this patch reduces the locked area
> in the IRQ handler only to these variables. Most of the code inside the
> locked area in the IRQ handler is not protected elsewhere; it means
> that it is not protected at all.
>
> Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
> ---
> drivers/ipack/devices/ipoctal.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/ipack/devices/ipoctal.c b/drivers/ipack/devices/ipoctal.c
> index 141094e..69687f1 100644
> --- a/drivers/ipack/devices/ipoctal.c
> +++ b/drivers/ipack/devices/ipoctal.c
> @@ -177,19 +177,20 @@ static void ipoctal_irq_tx(struct ipoctal_channel *channel)
> if (channel->nb_bytes == 0)
> return;
>
> + spin_lock(&channel->lock);
> value = channel->tty_port.xmit_buf[*pointer_write];
> iowrite8(value, &channel->regs->w.thr);
> channel->stats.tx++;
> (*pointer_write)++;
> *pointer_write = *pointer_write % PAGE_SIZE;
> channel->nb_bytes--;
> + spin_unlock(&channel->lock);
> }
>
> static void ipoctal_irq_channel(struct ipoctal_channel *channel)
> {
> u8 isr, sr;
>
> - spin_lock(&channel->lock);
> /* The HW is organized in pair of channels. See which register we need
> * to read from */
> isr = ioread8(&channel->block_regs->r.isr);
> @@ -213,8 +214,6 @@ static void ipoctal_irq_channel(struct ipoctal_channel *channel)
> /* TX of each character */
> if ((isr & channel->isr_tx_rdy_mask) && (sr & SR_TX_READY))
> ipoctal_irq_tx(channel);
> -
> - spin_unlock(&channel->lock);
> }
>
> static irqreturn_t ipoctal_irq_handler(void *arg)

Acked-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>

Sam
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