workqueue: stronger test in process_one_work()

After the recent changes, when POOL_DISASSOCIATED is cleared, the
running worker's local CPU should be the same as pool->cpu without any
exception even during cpu-hotplug.  Update the sanity check in
process_one_work() accordingly.

This patch changes "(proposition_A && proposition_B && proposition_C)"
to "(proposition_B && proposition_C)", so if the old compound
proposition is true, the new one must be true too. so this will not
hide any possible bug which can be caught by the old test.

tj: Minor updates to the description.

CC: Jason J. Herne <jjherne@linux.vnet.ibm.com>
CC: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -2020,13 +2020,8 @@ __acquires(&pool->lock)
 
 	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
 #endif
-	/*
-	 * Ensure we're on the correct CPU.  DISASSOCIATED test is
-	 * necessary to avoid spurious warnings from rescuers servicing the
-	 * unbound or a disassociated pool.
-	 */
-	WARN_ON_ONCE(!(worker->flags & WORKER_UNBOUND) &&
-		     !(pool->flags & POOL_DISASSOCIATED) &&
+	/* ensure we're on the correct CPU */
+	WARN_ON_ONCE(!(pool->flags & POOL_DISASSOCIATED) &&
 		     raw_smp_processor_id() != pool->cpu);
 
 	/*