sysmon(9): Fix mistake in sysmon_task_queue_barrier.

Need to allocate the task structure with malloc(9), not on the stack;
the task thread will free it with free(9). Forgot to squash this
into prev

sysmon(9): Fix mistake in sysmon_task_queue_barrier.

Need to allocate the task structure with malloc(9), not on the stack;
the task thread will free it with free(9). Forgot to squash this
into previous commit.

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sysmon(9): New sysmon_task_queue_barrier(pri) function.

This waits for the completion of all tasks at priority pri or lower
that are currently queued at the time of the call.

sysmon: Delete trailing whitespace. No functional change intended.

Typos.

sysmon_task_queue_sched needs to RUN_ONCE(tq_preinit) as well, it can
be called from sysmon_envsys_register() early.

Replace a home-grown run-once implementation with the real RUN_ONCE()

This really does need to return an error code, so change the
sysmon_task_queue_fini() function to have a non-void type.

It's a function returning void; don't return an error code.

Modularize sysmon and its components

Rearrange code in the sysmon queue execution thread to simplify locking logic.
Removes unreachable code warning.

Pass KTHREAD_MPSAFE to kthread_create(). I've been testing this for
some weeks in both UP and SMP without any issue so far.

Start detangling lock.h from intr.h. This is likely to cause short term
breakage, but the mess of dependencies has been regularly breaking the
build recently anyhow.

Match the docs: MUTEX_DRIVER/SPIN are now only for porting code written
for Solaris.

Convert sysmon_taskqueue to use mutex(9) and condvar(9) and initialize
them in init_main.c via sysmon_task_queue_preinit().

Reviewed and ok by ad@.

Merge some of the less invasive changes from the vmlocking branch:

- kthread, callout, devsw API changes
- select()/poll() improvements
- miscellaneous MT safety improvements

Use aprint_debug rather than printf for the annoying message
"WARNING: Callback scheduled before sysmon task queue thread present.".

__unused removal on arguments; approved by core.

- sprinkle __unused on function decls.
- fix a couple of unused bugs
- no more -Wno-unused for i386

merge ktrace-lwp.

- add const
- avoid variable shadowing.

Rename the thread command name so that it fits on top's display.

add missing __KERNEL_RCSID()

Generic "task queue" for sysmon back-ends. This provides a thread
context for callbacks that require it in order to handle sysmon-related
events.

Adapted from the "OsdSchedule" bits of the ACPI cod

Generic "task queue" for sysmon back-ends. This provides a thread
context for callbacks that require it in order to handle sysmon-related
events.

Adapted from the "OsdSchedule" bits of the ACPI code.

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