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`SpinLock`'s backend can be used for `SpinLockIrq`, if the interrupts are disabled. And it actually provides performance gains since interrupts are not needed to be disabled anymore. So add `Backend::BackendInContext` to describe the case where one backend can be used for another. Use the it to implement the `lock_with()` so that `SpinLockIrq` can avoid disabling interrupts by using `SpinLock`'s backend. Signed-off-by:Boqun Feng <boqun.feng@gmail.com>
`SpinLock`'s backend can be used for `SpinLockIrq`, if the interrupts are disabled. And it actually provides performance gains since interrupts are not needed to be disabled anymore. So add `Backend::BackendInContext` to describe the case where one backend can be used for another. Use the it to implement the `lock_with()` so that `SpinLockIrq` can avoid disabling interrupts by using `SpinLock`'s backend. Signed-off-by:
