# Re: \[RFC v4 01/11\] eventfd: Increase the recursion depth of eventfd\_signal()

- From: Jason Wang \<hidden\>
- Date: 2021-03-02 12:06:24 
- List: netdev
- Page: https://ratatoskr.run/netdev/2021/03/200892
- Thread: https://ratatoskr.run/netdev/2021/02/200438/t.md

```text

On 2021/2/23 7:50 下午, Xie Yongji wrote:
> Increase the recursion depth of eventfd_signal() to 1. This
> is the maximum recursion depth we have found so far.
>
> Signed-off-by: Xie Yongji <redacted>


Acked-by: Jason Wang <redacted>

It might be useful to explain how/when we can reach for this condition.

Thanks


> ---
>   fs/eventfd.c            | 2 +-
>   include/linux/eventfd.h | 5 ++++-
>   2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/fs/eventfd.c b/fs/eventfd.c
> index e265b6dd4f34..cc7cd1dbedd3 100644
> --- a/fs/eventfd.c
> +++ b/fs/eventfd.c
> @@ -71,7 +71,7 @@ __u64 eventfd_signal(struct eventfd_ctx *ctx, __u64 n)
>   	 * it returns true, the eventfd_signal() call should be deferred to a
>   	 * safe context.
>   	 */
> -	if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count)))
> +	if (WARN_ON_ONCE(this_cpu_read(eventfd_wake_count) > EFD_WAKE_DEPTH))
>   		return 0;
>   
>   	spin_lock_irqsave(&ctx->wqh.lock, flags);
> diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
> index fa0a524baed0..886d99cd38ef 100644
> --- a/include/linux/eventfd.h
> +++ b/include/linux/eventfd.h
> @@ -29,6 +29,9 @@
>   #define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
>   #define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
>   
> +/* Maximum recursion depth */
> +#define EFD_WAKE_DEPTH 1
> +
>   struct eventfd_ctx;
>   struct file;
>   
> @@ -47,7 +50,7 @@ DECLARE_PER_CPU(int, eventfd_wake_count);
>   
>   static inline bool eventfd_signal_count(void)
>   {
> -	return this_cpu_read(eventfd_wake_count);
> +	return this_cpu_read(eventfd_wake_count) > EFD_WAKE_DEPTH;
>   }
>   
>   #else /* CONFIG_EVENTFD */

```