Is there any difference between SeqCst store and SeqCst fence after a Relaxed store?

[MrCroxx]

Hi team, I'm currently learning the source code of the cool crossbeam-epoch and I found some questions.

When marking the global epoch as pinned, a SeqCst memory-ordered store operation is needed. I found in crossbeam-epoch it first performed a Relaxed store then send a SeqCst fence manually. Is there any difference between just using a SeqCst store here?

crossbeam/crossbeam-epoch/src/internal.rs

Lines 425 to 426 in 94e0400

	self.epoch.store(new_epoch, Ordering::Relaxed);
	atomic::fence(Ordering::SeqCst);

[zhangzhuang15]

I guess that it only works for 'epoch' variable:

self.epoch.store(new_epoch, Ordering::SeqCst);

But it also works other variables which adapt "Ordering::SeqCst" by using fence of "Ordering::SeqCst"