On 3/12/22 20:59, Warner Losh wrote:
> FreeBSD's pthread_mutex is shared between the kernel and user land.
> So it does a compare and set to take the lock. Uncontested and unheld
> locks will mean we've taken the lock and return. Contested locks
> are kicked to the kernel to wait. When userland releases the lock
> it signals the kernel to wakeup via a system call. The kernel then
> does a cas to try to acquire the lock. It either returns with the lock
> held, or goes back to sleep. This we have atomics operating both in
> the kernel (via standard host atomics) and userland atomics done
> via start/end_exclusive.
You need to use standard host atomics for this case.
Or use the start/end_exclusive for both by emulating the kernel call, I presume? It's the mixing that's the problem, right?
WarnerÂ