b9cedb46e2
The SCHEDULER_STOPPED() hack breaks locking generally, and mtx_trylock_*() especially. When mtx_trylock_*() returns nonzero, naive code version here trusts it to have worked. But when SCHEDULER_STOPPED() is true, mtx_trylock_*() returns 1 without doing anything. Then mtx_unlock_*() crashes especially badly attempting to unlock iff the error is detected, since mutex unlocking functions don't check SCHEDULER_STOPPED(). syscons already didn't trust mtx_trylock_spin(), but it was missing the logic to turn on sp->kdb_locked when turning off sp->mtx_locked during panics. It also used panicstr instead of SCHEDULER_LOCKED because I thought that panicstr was more fragile. They only differ for a window of lines in panic(), and in broken cases where stop_cpus_hard() in panic() didn't work.
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