In bufdone_finish() restrict the acquisition and release of the page queues lock to BIO_READ operations.  Recent changes to the implementation of the per-page flags have eliminated the need for the page queues lock in the other cases.
In bufdone_finish() restrict the acquisition and release of the page
queues lock to BIO_READ operations.  Recent changes to the implementation
of the per-page flags have eliminated the need for the page queues lock
in the other cases.

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