sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

rms: add rms_assert_rlock_ok

So that callers which opportunistically elide the lock can still
assert that they can take it.

Reviewed by:
Differential Revision:

rmlock(9): add an RM_DUPOK flag

Allows for duplicate locks to be acquired without witness complaining.
Similar flags exists already for rwlock(9) and sx(9).

Reviewed by: markj
MFC after: 3 days
Sponsored by: NetApp, Inc.
Sponsored by: Klara, Inc.
NetApp PR: 52
Differential Revision: https://reviews.freebsd.org/D29683n

rms: several cleanups + debug read lockers handling

This adds a dedicated counter updated with atomics when INVARIANTS
is used. As a side effect one can reliably determine the lock is held
for reading by at least one thread, but it's still not possible to
find out whether curthread has the lock in said mode.

This should be good enough in practice.

Problem spotted by avg.

rms: fixup concurrent writer handling and add more features

Previously the code had one wait channel for all pending writers.
This could result in a buggy scenario where after a writer switches
the lock mode form readers to writers goes off CPU, another writer
queues itself and then the last reader wakes up the latter instead
of the former.

Use a separate channel.

While here add features to reliably detect whether curthread has
the lock write-owned. This will be used by ZFS.

Add rms_try_rlock and rms_wowned.

Add read-mostly sleepable locks

To be used when like rmlocks, except when sleeping for readers needs to be
allowed. See the manpage for more information.

Reviewed by: kib (previous version)
Differential Revision: https://reviews.freebsd.org/D22823

Remove unused *_sysinit_flags() declarations.

Submitted by: Sebastian Huber <sebastian.huber@embedded-brains.de>
MFC after: 3 days

Clean up the SYSINIT_FLAGS definitions for rwlock(9) and rmlock(9).

Avoid duplication in their macro definitions, and document them. No
functional change intended.

MFC after: 1 week

sys: further adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 3-Clause license.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

Special thanks to Wind River for providing access to "The Duke of
Highlander" tool: an older (2014) run over FreeBSD tree was useful as a
starting point.

Add _NEW flag to mtx(9), sx(9), rmlock(9) and rwlock(9).
A _NEW flag passed to _init_flags() to avoid check for double-init.

Differential Revision: https://reviews.freebsd.org/D1208
Reviewed by: jhb, wblock
MFC after: 1 Month

Several improvements to rmlock(9). Many of these are based on patches
provided by Isilon.
- Add an rm_assert() supporting various lock assertions similar to other
locking primitives. Because rmlocks track readers the assertions are
always fully accurate unlike rw_assert() and sx_assert().
- Flesh out the lock class methods for rmlocks to support sleeping via
condvars and rm_sleep() (but only while holding write locks), rmlock
details in 'show lock' in DDB, and the lc_owner method used by
dtrace.
- Add an internal destroyed cookie so that API functions can assert
that an rmlock is not destroyed.
- Make use of rm_assert() to add various assertions to the API (e.g.
to assert locks are held when an unlock routine is called).
- Give RM_SLEEPABLE locks their own lock class and always use the
rmlock's own lock_object with WITNESS.
- Use THREAD_NO_SLEEPING() / THREAD_SLEEPING_OK() to disallow sleeping
while holding a read lock on an rmlock.

Submitted by: andre
Obtained from: EMC/Isilon

Replace the TDP_NOSLEEPING flag with a counter so that the
THREAD_NO_SLEEPING() and THREAD_SLEEPING_OK() macros can nest.

Reviewed by: attilio

Constify arguments for locking KPIs where possible.

This enables locking consumers to pass their own structures around as const and
be able to assert locks embedded into those structures.

Reviewed by: ed, kib, jhb

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

rmlock(9) two additions and one change/fix:
- add rm_try_rlock().
- add RM_SLEEPABLE to use sx(9) as the back-end lock in order to sleep while
holding the write lock.
- change rm_noreadtoken to a cpu bitmask to indicate which CPUs need to go
through the lock/unlock in order to synchronize. As a side effect, this
also avoids IPI to CPUs without any readers during rm_wlock.

Discussed with: ups@, rwatson@ on arch@
Sponsored by: Isilon Systems, Inc.

Make the rmlock(9) interface a bit more like the rwlock(9) interface:

- Add rm_init_flags() and accept extended options only for that variation.
- Add a flags space specifically for rm_init_flags(), rather than borrowing
the lock_init() flag space.
- Define flag RM_RECURSE to use instead of LO_RECURSABLE.
- Define flag RM_NOWITNESS to allow an rmlock to be exempt from WITNESS
checking; this wasn't possible previously as rm_init() always passed
LO_WITNESS when initializing an rmlock's struct lock.
- Add RM_SYSINIT_FLAGS().
- Rename embedded mutex in rmlocks to make it more obvious what it is.
- Update consumers.
- Update man page.

Reduce vertical whitespace and other minor style tweaks.

Remove unused rm_initialized() macro.

- Import the HEAD csup code which is the basis for the cvsmode work.

Add rm_wowned(9) function to test whether the current thread owns an
exclusive lock on the passed rmlock.

Reviewed by: ups

Initial checkin for rmlock (read mostly lock) a multi reader single writer
lock optimized for almost exclusive reader access. (see also rmlock.9)

TODO:
Convert to per cpu variables linkerset as soon as it is available.
Optimize UP (single processor) case.