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SubjectRe: [KVM PATCH v9 2/5] eventfd: use locked POLLHUP
On Thu, 2 Jul 2009, Gregory Haskins wrote:

> eventfd currently emits a POLLHUP wakeup on f_ops->release() to generate a
> "release" callback. This lets eventfd clients know if the eventfd is about
> to go away and is very useful particularly for in-kernel clients. However,
> as it stands today it is not possible to use this feature of eventfd in a
> race-free way. This patch changes the POLLHUP code to use the locked variant
> to rectify this problem.
>
> Signed-off-by: Gregory Haskins <ghaskins@novell.com>
> CC: Davide Libenzi <davidel@xmailserver.org>
> ---
>
> fs/eventfd.c | 7 +------
> 1 files changed, 1 insertions(+), 6 deletions(-)
>
> diff --git a/fs/eventfd.c b/fs/eventfd.c
> index d9849a1..31d12de 100644
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -105,12 +105,7 @@ static int eventfd_release(struct inode *inode, struct file *file)
> {
> struct eventfd_ctx *ctx = file->private_data;
>
> - /*
> - * No need to hold the lock here, since we are on the file cleanup
> - * path and the ones still attached to the wait queue will be
> - * serialized by wake_up_locked_poll().
> - */
> - wake_up_locked_poll(&ctx->wqh, POLLHUP);
> + wake_up_poll(&ctx->wqh, POLLHUP);
> eventfd_ctx_put(ctx);
> return 0;
> }

ACK.
BTW, mainline already has the correct wake_up_poll().


- Davide




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