block: Check locking assumptions at runtime

block: Check locking assumptions at runtime

Instead of documenting the locking assumptions of most block layer
functions as a comment, use lockdep_assert_held() to verify locking
assumptions at runtime.

Signed-off-by: Bart Van Assche <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Omar Sandoval <[email protected]>
Cc: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>