Prevent live-lock and access of destroyed data in taskqueue_drain_all().

Phabric:	https://reviews.freebsd.org/D1247
Reviewed by:	jhb, avg
Sponsored by:	Spectra Logic Corporation

sys/kern_subr_taskqueue.c:
	Modify taskqueue_drain_all() processing to use a temporary
	"barrier task", rather than rely on a user task that may
	be destroyed during taskqueue_drain_all()'s execution.  The
	barrier task is queued behind all previously queued tasks
	and then has its priority elevated so that future tasks
	cannot pass it in the queue.

	Use a similar barrier scheme to drain threads processing
	current tasks.  This requires taskqueue_run_locked() to
	insert and remove the taskqueue_busy object for the running
	thread for every task processed.

share/man/man9/taskqueue.9:
	Remove warning about live-lock issues with taskqueue_drain_all()
	and indicate that it does not wait for tasks queued after
	it begins processing.

0 files changed, 0 insertions, 0 deletions