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SubjectRe: [PATCH] Input: fixed EVIOCGRAB iterative grab/release.
Hi Terry,

> Fixed order of calls in evdev_ungrab to allow iterative use of
> code which grabs and releases input event devices.
>
> Signed-off-by: Terry Lambert <tlambert@chromium.org>
> ---
> drivers/input/evdev.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index c8471a2..0bac8da 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -160,9 +160,9 @@ static int evdev_ungrab(struct evdev *evdev, struct evdev_client *client)
> if (evdev->grab != client)
> return -EINVAL;
>
> + input_release_device(&evdev->handle);
> rcu_assign_pointer(evdev->grab, NULL);
> synchronize_rcu();
> - input_release_device(&evdev->handle);

I imagine the current code could lead to a race situation if there
were no other locks involved. However, evdev_ungrab() is always called
under evdev->mutex. As Dmitry hinted, grabbing "usually works", so
perhaps you could device a tiny program which reproduces the problem?

Thanks,
Henrik


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