md: check arrays is suspended in mddev_detach before call quiesce operations

Don't call quiesce(1) and quiesce(0) if array is already suspended,
otherwise in level_store, the array is writable after mddev_detach
in below part though the intention is to make array writable after
resume.

	mddev_suspend(mddev);
	mddev_detach(mddev);
	...
	mddev_resume(mddev);

And it also causes calltrace as follows in [1].

[48005.653834] WARNING: CPU: 1 PID: 45380 at kernel/kthread.c:510 kthread_park+0x77/0x90
[...]
[48005.653976] CPU: 1 PID: 45380 Comm: mdadm Tainted: G           OE     5.4.10-arch1-1 #1
[48005.653979] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./J4105-ITX, BIOS P1.40 08/06/2018
[48005.653984] RIP: 0010:kthread_park+0x77/0x90
[48005.654015] Call Trace:
[48005.654039]  r5l_quiesce+0x3c/0x70 [raid456]
[48005.654052]  raid5_quiesce+0x228/0x2e0 [raid456]
[48005.654073]  mddev_detach+0x30/0x70 [md_mod]
[48005.654090]  level_store+0x202/0x670 [md_mod]
[48005.654099]  ? security_capable+0x40/0x60
[48005.654114]  md_attr_store+0x7b/0xc0 [md_mod]
[48005.654123]  kernfs_fop_write+0xce/0x1b0
[48005.654132]  vfs_write+0xb6/0x1a0
[48005.654138]  ksys_write+0x67/0xe0
[48005.654146]  do_syscall_64+0x4e/0x140
[48005.654155]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[48005.654161] RIP: 0033:0x7fa0c8737497

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=206161

Signed-off-by: Guoqing Jiang <[email protected]>
Signed-off-by: Song Liu <[email protected]>

Author: Guoqing Jiang

drivers/md/md.c

@@ -6184,7 +6184,7 @@ EXPORT_SYMBOL_GPL(md_stop_writes);
 static void mddev_detach(struct mddev *mddev)
 {
 	md_bitmap_wait_behind_writes(mddev);
-	if (mddev->pers && mddev->pers->quiesce) {
+	if (mddev->pers && mddev->pers->quiesce && !mddev->suspended) {
 		mddev->pers->quiesce(mddev, 1);
 		mddev->pers->quiesce(mddev, 0);
 	}