Instead of using a simple switch to determine if preemption is enabled
(`is_preemptable: bool`), a counter is used instead. This handles the
case where a function holding a `PreemptGuard` calls another function
that creates a new `PreemptGuard`.
Signed-off-by: Anhad Singh <andypython@protonmail.com>
The global allocator panics when out of memory rather than returning an
errors. In addition there are plenty of other places where we don't
handle allocation failure anyway. At some point in the future we should
systematically handle out of memory conditions, but until then let's not
pretend we do and get rid of the usage of the unstable allocator_api
feature that is unlikely to get stabilized any time soon.
Technically there should be an atomic and nonatomic set type, but perf
should be the same, as the nonatomic one would only be used when setting
the sched_affinity.
The spin crate considers it UB to call force_write_unlock while there is
a threads trying to obtain a read lock on the same rwlock.
This also switches to the spinning_lot crate for the context rwlock as
it has support for a write guard keeping a reference to the rwlock using
an Arc instead of a reference.
Previously there was a triple fault, due to a combination of reasons
(e.g. rsp and rbp being ordered in the struct and in the assembly).
Now, the locks will be held __all the way until the new context__ has
been switched to, which completely eliminates any possibility that the
"pcid fault" originates here.
While I am unsure whether this will work, this could also be an
opportunity to be able to remove CONTEXT_SWITCH_LOCK fully.
Most of this was generated by the absolutely extraordinary `cargo fix`
subcommand. There were still 2 errors and a few warnings to patch up,
but compared to the normal 600+ errors, I'd say the fixer did a damn
good job! I'm also amazed that I could still start the VM after this,
I half expected some kinds of runtime failure...
Anhad Singh