workqueue: wake up a worker when a rescuer is leaving a gcwq

commit 7576958a9d5a4a677ad7dd40901cdbb6c1110c98 upstream.

After executing the matching works, a rescuer leaves the gcwq whether
there are more pending works or not.  This may decrease the
concurrency level to zero and stall execution until a new work item is
queued on the gcwq.

Make rescuer wake up a regular worker when it leaves a gcwq if there
are more works to execute, so that execution isn't stalled.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Ray Jui <rjui@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>