The lock loop does:
sevl
wfe
ldaxr
if locked: cbnz ... 1b → back to wfe
But there is no corresponding sev anywhere in spin_unlock(). If another CPU releases the lock without generating an event, a waiter may sit in wfe until some unrelated event occurs (timer tick, interrupt, other SEV somewhere), which is not guaranteed in all contexts (especially if interrupts are disabled, or in early boot, or in some low-noise situations).
This is a liveness bug: you can get “lock released but nobody wakes”.
The lock loop does:
sevl
wfe
ldaxr
if locked: cbnz ... 1b → back to wfe
But there is no corresponding sev anywhere in spin_unlock(). If another CPU releases the lock without generating an event, a waiter may sit in wfe until some unrelated event occurs (timer tick, interrupt, other SEV somewhere), which is not guaranteed in all contexts (especially if interrupts are disabled, or in early boot, or in some low-noise situations).
This is a liveness bug: you can get “lock released but nobody wakes”.