Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add some cross references to locking.9 from related pages.

Xref rwlock(9).

Reviewed by: ru

mdoc(7) fixes.

Update the .Dd date for previous commit.

Gently nudged by: krion

Change the return value of sema_timedwait() so it returns 0 on
success and a proper errno value on failure. This makes it
consistent with cv_timedwait(), and paves the way for the
introduction of functions such as sema_timedwait_sig() which can
fail in multiple ways.

Bump __FreeBSD_version and add a note to UPDATING.

Approved by: scottl (ips driver), arch

Add mtx_pool(9) to the SEE ALSO section.

Submitted by: Garrett Rooney <rooneg@electricjellyfish.net>

Update function definitions and required include files to reflect
the current state of the system.

Approved by: alfred

Fixed missing include in synopsis.

Common Mike adds see alsos from all of the synchronization
man pages to their brethren.

mdoc(7) police: minor markup fixes.

Implement kernel semaphores.

Reviewed by: jhb