kernel: throne_tracker: offload to kthread tiann #2632

Run throne_tracker() in kthread instead of blocking the caller.
Prevents full lockup during installation and removing the manager.

By default, first run remains synchronous for compatibility purposes
(FDE, FBEv1, FBEv2)

Features:
- looks and waits for manager UID in /data/system/packages.list
- run track_throne() in a kthread after the first synchronous run
- prevent duplicate thread creation with a single-instance check
- spinlock-on-d_lock based polling adressing possible race conditions.

Race conditions adressed
- single instance kthread lock, smp_mb()
- track_throne_function, packages.list, spinlock-on-d_lock based polling
- is_manager_apk, apk, spinlock-on-d_lock based polling

This is a squash of:
https://github.com/tiann/KernelSU/pull/2632

Original skeleton based on:
`kernelsu: move throne_tracker() to kthread`
`kernelsu: check locking before accessing files and dirs during searching manager`
`kernelsu: look for manager UID in /data/system/packages.list, not /data/system/packages.list.tmp`
0b05e927...8783badd

Co-Authored-By: backslashxx <118538522+backslashxx@users.noreply.github.com>
Co-Authored-By: Yaroslav Zviezda <10716792+acroreiser@users.noreply.github.com>
Signed-off-by: backslashxx <118538522+backslashxx@users.noreply.github.com>

kernel/Kconfig

@@ -59,6 +59,15 @@ config KSU_LSM_SECURITY_HOOKS
 	  Disabling this is mostly only useful for kernel 4.1 and older.
 	  Make sure to implement manual hooks on security/security.c.
 
+config KSU_THRONE_TRACKER_ALWAYS_THREADED
+	bool "Always run throne_tracker in a kthread"
+	default n
+	help
+	  Runs throne_tracker in a separate kthread, including the first run.
+	  Significantly decreases boot time, but can cause crowning failure
+	  on some FDE or FBEv1 setups.
+	  If unsure, say n.
+
 choice
 	prompt "KernelSU hook type"
 	depends on KSU