On Fri, Mar 16, 2012 at 09:04:29PM +0100, David Herrmann wrote:
> Consider two threads calling read() on the same uinput-fd, both
> non-blocking. Assume there is data-available so both will simultaneously
> pass:
> udev->head == udev->tail
> Then the first thread goes to sleep and the second one pops the message
> from the queue. Now assume udev->head == udev->tail. If the first thread
> wakes up it will call wait_event_*() and sleep in the waitq. This
> effectively turns the non-blocking FD into a blocking one.
>
> We fix this by never calling wait_event_*() for non-blocking FDs hence we
> will never sleep in the waitq here.
>
> Signed-off-by: David Herrmann <dh.herrmann@xxxxxxxxxxxxxx>
> ---
> drivers/input/misc/uinput.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
> index 7360568..1526814 100644
> --- a/drivers/input/misc/uinput.c
> +++ b/drivers/input/misc/uinput.c
> @@ -460,13 +460,15 @@ static ssize_t uinput_read(struct file *file, char __user *buffer, size_t count,
> if (udev->state != UIST_CREATED)
> return -ENODEV;
>
> - if (udev->head == udev->tail && (file->f_flags & O_NONBLOCK))
> - return -EAGAIN;
> -
> - retval = wait_event_interruptible(udev->waitq,
> + if (file->f_flags & O_NONBLOCK) {
> + if (udev->head == udev->tail)
> + return -EAGAIN;
> + } else {
> + retval = wait_event_interruptible(udev->waitq,
> udev->head != udev->tail || udev->state != UIST_CREATED);
> - if (retval)
> - return retval;
> + if (retval)
> + return retval;
> + }
>
> retval = mutex_lock_interruptible(&udev->mutex);
> if (retval)
makes sense, patch looks good
Acked-by: Aristeu Rozanski <aris@xxxxxxxxx>
--
Aristeu
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