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>
> ---
> drivers/input/serio/serio_raw.c | 43 ++++++++++++++++++++++----------------
> 1 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,
> struct serio_raw *serio_raw = client->serio_raw;
> char uninitialized_var(c);
> ssize_t read = 0;
> - int retval;
> + int error = 0;
>
> - if (serio_raw->dead)
> - return -ENODEV;
> + do {
> + if (serio_raw->dead)
> + return -ENODEV;
>
> - if (serio_raw->head == serio_raw->tail && (file->f_flags & O_NONBLOCK))
> - return -EAGAIN;
> + if (serio_raw->head == serio_raw->tail &&
> + (file->f_flags & O_NONBLOCK))
> + return -EAGAIN;
>
> - retval = wait_event_interruptible(serio_raw->wait,
> - serio_raw->head != serio_raw->tail || serio_raw->dead);
> - if (retval)
> - return retval;
> + if (count == 0)
> + break;
>
> - if (serio_raw->dead)
> - return -ENODEV;
> + while (read < count && serio_raw_fetch_byte(serio_raw, &c)) {
> + if (put_user(c, buffer++)) {
> + error = -EFAULT;
> + goto out;
> + }
> + read++;
> + }
>
> - while (read < count && serio_raw_fetch_byte(serio_raw, &c)) {
> - if (put_user(c, buffer++)) {
> - retval = -EFAULT;
> + if (read)
> break;
> - }
> - read++;
> - }
>
> - return read ?: retval;
> + if (!(file->f_flags & O_NONBLOCK))
> + error = wait_event_interruptible(serio_raw->wait,
> + serio_raw->head != serio_raw->tail ||
> + serio_raw->dead);
> + } while (!error);
> +
> +out:
> + return read ?: error;
> }
>
> static ssize_t serio_raw_write(struct file *file, const char __user *buffer,
> --
> 1.7.7.6
>
>
> --
> Dmitry
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