Man page 9 : try_wait_for_completion

try_wait_for_completion - try to decrement a completion without blocking

bool try_wait_for_completion(struct completion *  x );

x
    completion structure

0 if a decrement cannot be done without blocking 1 if a decrement succeeded.

If a completion is being used as a counting completion, attempt to decrement the counter without blocking. This enables us to avoid waiting if the resource the completion is protecting is not available.