tokio::sync::Notify is not Unwind Safe

[zicklag]

Version
1.21.2

Platform
Rust playground and Linux, Ubuntu 20.04.

Description
I was trying to catch_unwind in a project depending on Tokio's tokio::sync::Notify primitive, and ran into a compile error because Notify is not unwind safe.

I'm not sure if this is technically a bug or a feature request.

I tried this code:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c1409cc70ceea71c7d28c41f7232e19c

#[tokio::main]
async fn main() {
    let notify = tokio::sync::Notify::new();
    
    std::panic::catch_unwind(|| {
        notify.notify_one();
    });
}

I expected to see this happen: No compile error

Instead, this happened:

Compiling playground v0.0.1 (/playground)
error[[E0277]](https://doc.rust-lang.org/stable/error-index.html#E0277): the type `UnsafeCell<AtomicUsize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
 --> src/main.rs:5:5
  |
5 |     std::panic::catch_unwind(|| {
  |     ^^^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<AtomicUsize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
  |
  = help: within `Notify`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<AtomicUsize>`
  = note: required because it appears within the type `tokio::loom::std::atomic_usize::AtomicUsize`
  = note: required because it appears within the type `Notify`
  = note: required because of the requirements on the impl of `UnwindSafe` for `&Notify`
note: required because it's used within this closure
 --> src/main.rs:5:30
  |
5 |     std::panic::catch_unwind(|| {
  |                              ^^
note: required by a bound in `catch_unwind`

error[[E0277]](https://doc.rust-lang.org/stable/error-index.html#E0277): the type `UnsafeCell<tokio::util::linked_list::LinkedList<tokio::sync::notify::Waiter, tokio::sync::notify::Waiter>>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
 --> src/main.rs:5:5
  |
5 |     std::panic::catch_unwind(|| {
  |     ^^^^^^^^^^^^^^^^^^^^^^^^ `UnsafeCell<tokio::util::linked_list::LinkedList<tokio::sync::notify::Waiter, tokio::sync::notify::Waiter>>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
  |
  = help: within `Notify`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<tokio::util::linked_list::LinkedList<tokio::sync::notify::Waiter, tokio::sync::notify::Waiter>>`
  = note: required because it appears within the type `lock_api::mutex::Mutex<parking_lot::raw_mutex::RawMutex, tokio::util::linked_list::LinkedList<tokio::sync::notify::Waiter, tokio::sync::notify::Waiter>>`
  = note: required because it appears within the type `tokio::loom::std::parking_lot::Mutex<tokio::util::linked_list::LinkedList<tokio::sync::notify::Waiter, tokio::sync::notify::Waiter>>`
  = note: required because it appears within the type `Notify`
  = note: required because of the requirements on the impl of `UnwindSafe` for `&Notify`
note: required because it's used within this closure
 --> src/main.rs:5:30
  |
5 |     std::panic::catch_unwind(|| {
  |                              ^^
note: required by a bound in `catch_unwind`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` due to 2 previous errors

[Darksonn]

Sure, we can do that.