GC Deadlock: IL2CPP threads blocked on SuspendSemaphore/work semaphores (Arcade Game Zone)

[jackby03]

Symptoms

• Game: Arcade Game Zone (PPSA19015) - Unity/IL2CPP
• 13 AssetGarbageCollectorHelper threads blocked on sceKernelWaitSema (work semaphores)
• 1 coordinator thread blocked on sceKernelWaitSema (SuspendSemaphore)
• Main thread blocked on handshake semaphore
• Stall detected after 20s, exit code 4

Log evidence

[LOADER][ERROR] Stall import-stub: rip=0x00006FFFFD000EE0 nid=Zxa0VhQVTsk -> libKernel:sceKernelWaitSema
[LOADER][ERROR] Stall guest-thread: handle=0x00000207AC514E50 name='AssetGarbageCollectorHelper' state=Blocked imports=24 nid=Zxa0VhQVTsk block=sceKernelWaitSema
[LOADER][ERROR] Stall guest-thread: handle=0x00000207AB5CD9A0 name='Thread-207AB5CD9A0' state=Blocked imports=38 nid=Zxa0VhQVTsk rdi=0x0000000000000083 block=sceKernelWaitSema
[LOADER][ERROR] Stall main-thread: managed_id=2 state=Blocked block=sceKernelWaitSema:0x00000081:Baselib_SystemSemaphore

Analysis

Circular deadlock in IL2CPP GC suspension: coordinator waits for workers to signal SuspendSemaphore, but workers wait for coordinator to signal work semaphores. No progress possible.

Possible causes

• sceKernelSuspendScheduler not implemented
• Race condition in semaphore implementation (fixed in [HLE/Kernel/Pad/Ngs2] Fix semaphore race condition, add main-thread diagnostics, implement missing pad/ngs2 imports #253 but didn't resolve this)
• Workers should be woken via a mechanism not yet supported