Re: [PATCH] Input: serio_raw - ensure we don't block in non-blocking read

[Che-liang Chiou]

I didn't test the patch, but the logic looks fine to me.

On Wed, Apr 4, 2012 at 4:24 AM, Dmitry Torokhov
<dmitry.torokhov@xxxxxxxxx> wrote:
> Avoid calling wait_event_interruptible() if client requested non-blocking
> read, since it is not guaranteed that another thread will not consume
> event after we checked if serio_raw->head != serio_raw->tail.
>
> Also ensure we do not return 0 but keep waiting instead in blocking case,
> when another thread steals "our" byte.
>
> Signed-off-by: Dmitry Torokhov <dtor@xxxxxxx>
> ---
> Âdrivers/input/serio/serio_raw.c | Â 43 ++++++++++++++++++++++----------------
> Â1 files changed, 25 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/input/serio/serio_raw.c b/drivers/input/serio/serio_raw.c
> index 4494233..094d6fb 100644
> --- a/drivers/input/serio/serio_raw.c
> +++ b/drivers/input/serio/serio_raw.c
> @@ -165,31 +165,38 @@ static ssize_t serio_raw_read(struct file *file, char __user *buffer,
> Â Â Â Âstruct serio_raw *serio_raw = client->serio_raw;
> Â Â Â Âchar uninitialized_var(c);
> Â Â Â Âssize_t read = 0;
> - Â Â Â int retval;
> + Â Â Â int error = 0;
>
> - Â Â Â if (serio_raw->dead)
> - Â Â Â Â Â Â Â return -ENODEV;
> + Â Â Â do {
> + Â Â Â Â Â Â Â if (serio_raw->dead)
> + Â Â Â Â Â Â Â Â Â Â Â return -ENODEV;
>
> - Â Â Â if (serio_raw->head == serio_raw->tail && (file->f_flags & O_NONBLOCK))
> - Â Â Â Â Â Â Â return -EAGAIN;
> + Â Â Â Â Â Â Â if (serio_raw->head == serio_raw->tail &&
> + Â Â Â Â Â Â Â Â Â (file->f_flags & O_NONBLOCK))
> + Â Â Â Â Â Â Â Â Â Â Â return -EAGAIN;
>
> - Â Â Â retval = wait_event_interruptible(serio_raw->wait,
> - Â Â Â Â Â Â Â Â Â Â Â serio_raw->head != serio_raw->tail || serio_raw->dead);
> - Â Â Â if (retval)
> - Â Â Â Â Â Â Â return retval;
> + Â Â Â Â Â Â Â if (count == 0)
> + Â Â Â Â Â Â Â Â Â Â Â break;
>
> - Â Â Â if (serio_raw->dead)
> - Â Â Â Â Â Â Â return -ENODEV;
> + Â Â Â Â Â Â Â while (read < count && serio_raw_fetch_byte(serio_raw, &c)) {
> + Â Â Â Â Â Â Â Â Â Â Â if (put_user(c, buffer++)) {
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â error = -EFAULT;
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â goto out;
> + Â Â Â Â Â Â Â Â Â Â Â }
> + Â Â Â Â Â Â Â Â Â Â Â read++;
> + Â Â Â Â Â Â Â }
>
> - Â Â Â while (read < count && serio_raw_fetch_byte(serio_raw, &c)) {
> - Â Â Â Â Â Â Â if (put_user(c, buffer++)) {
> - Â Â Â Â Â Â Â Â Â Â Â retval = -EFAULT;
> + Â Â Â Â Â Â Â if (read)
> Â Â Â Â Â Â Â Â Â Â Â Âbreak;
> - Â Â Â Â Â Â Â }
> - Â Â Â Â Â Â Â read++;
> - Â Â Â }
>
> - Â Â Â return read ?: retval;
> + Â Â Â Â Â Â Â if (!(file->f_flags & O_NONBLOCK))
> + Â Â Â Â Â Â Â Â Â Â Â error = wait_event_interruptible(serio_raw->wait,
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â serio_raw->head != serio_raw->tail ||
> + Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â serio_raw->dead);
> + Â Â Â } while (!error);
> +
> +out:
> + Â Â Â return read ?: error;
> Â}
>
> Âstatic ssize_t serio_raw_write(struct file *file, const char __user *buffer,
> --
> 1.7.7.6
>
>
> --
> Dmitry
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