sched_ext: Add SCX_EFLAG_INITIALIZED to indicate successful ops.init()

ops.exit() may be called even if the loading failed before ops.init()
finishes successfully. This is because ops.exit() allows rich exit info
communication. Add SCX_EFLAG_INITIALIZED flag to scx_exit_info.flags to
indicate whether ops.init() finished successfully.

This enables BPF schedulers to distinguish between exit scenarios and
handle cleanup appropriately based on initialization state.

Acked-by: Andrea Righi <[e-mail]>
Signed-off-by: Tejun Heo <[e-mail]>

kernel/sched/ext.c

···
 			scx_error(sch, "ops.init() failed (%d)", ret);
 			goto err_disable;
 		}
+		sch->exit_info->flags |= SCX_EFLAG_INITIALIZED;
 	}
 
 	for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++)

kernel/sched/ext_internal.h

···
 	SCX_ECODE_ACT_RESTART	= 1LLU << 48,
 };
 
+enum scx_exit_flags {
+	/*
+	 * ops.exit() may be called even if the loading failed before ops.init()
+	 * finishes successfully. This is because ops.exit() allows rich exit
+	 * info communication. The following flag indicates whether ops.init()
+	 * finished successfully.
+	 */
+	SCX_EFLAG_INITIALIZED,
+};
+
 /*
  * scx_exit_info is passed to ops.exit() to describe why the BPF scheduler is
  * being disabled.
···
 
 	/* exit code if gracefully exiting */
 	s64			exit_code;
+
+	/* %SCX_EFLAG_* */
+	u64			flags;
 
 	/* textual representation of the above */
 	const char		*reason;