Add a waitqueue helper to add a priority waiter that requires exclusive
wakeups, i.e. that requires that it be the _only_ priority waiter. The
API will be used by KVM to ensure that at most one of KVM's irqfds is
bound to a single eventfd (across the entire kernel).
Open code the helper instead of using __add_wait_queue() so that the
common path doesn't need to "handle" impossible failures.
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250522235223.3178519-9-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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