ANDROID: Move SCX_OPS_DISABLING VH inside the scx_fork_rwsem section

We found a stability issue in current code of scx_ops_disable_workfn
founction. When SCX_OPS_DISABLING VH is invoked, system may keeps
forking fair tasks. In this circumstances, if scx_ops_disable_workfn
is blocked by scx_fork_rwsem, it may never running again because the
task who invoking scx_ops_disable_workfn is scx task.

So we move the SCX_OPS_DISABLING VH inside scx_fork_rwsem section.

This patchset ensures that if the scx task who invoking
scx_ops_disable_workfn is blocked by scx_fork_rwsem, the system will
not produce fair task. This can avoid the stability issue caused in
scx disabling process.

Bug: 439095466
Bug: 454747318

Change-Id: I16e67e868d8ba1a7f14309eab64b7d5d781e5ca9
Signed-off-by: ZhiFeng Gao <gaozhifeng@oppo.com>
(cherry picked from commit ad3375325ca2ff7356bdea0adec021abc29e23ff)

kernel/sched/ext.c

@@ -4645,7 +4645,6 @@ static void scx_ops_disable_workfn(struct kthread_work *work)
 	default:
 		break;
 	}
-	trace_android_vh_scx_ops_enable_state(SCX_OPS_DISABLING);
 
 	/*
 	 * Here, every runnable task is guaranteed to make forward progress and
@@ -4670,6 +4669,7 @@ static void scx_ops_disable_workfn(struct kthread_work *work)
 	 * must be switched out and exited synchronously.
 	 */
 	percpu_down_write(&scx_fork_rwsem);
+	trace_android_vh_scx_ops_enable_state(SCX_OPS_DISABLING);
 
 	scx_ops_init_task_enabled = false;