sync: add_permits does not panic with usize::MAX >> 3

[blasrodri]

Fixed incorrect shift in the assignment of permits on batch_semaphore.rs

Fixes: #3095

[Darksonn]

Can someone who knows the implementation of Semaphore confirm whether this line is also correct?

let prev = self.permits.fetch_add(rem << Self::PERMIT_SHIFT, Release);

It's just outside the area I can select with the diff tool.

[blasrodri]

Can someone who knows the implementation of Semaphore confirm whether this line is also correct?

let prev = self.permits.fetch_add(rem << Self::PERMIT_SHIFT, Release);

It's just outside the area I can select with the diff tool.

My guess is that that line is correct.
self.permits are always shifted while stored in the struct. But when manipulated, the shift is reverted. That's why, when they are stored again (in that line you mentioned), the shift occurs.

[hawkw]

This looks correct to me!

[Darksonn]

This also seems correct to me now.