The return-value convention for these functions varies depending on
whether they're interruptible or can timeout.  It can be a little
confusing--document it.
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111006192246.GB28026@fieldses.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>