Avoid potential deadlock in mullvad-api

[MarkusPettersson98]

This PR consolidates two mutexes found in the ApiAvailability struct into a single one. We managed to run into a deadlock once where mullvad-daemon would not progress from the Disconnecting state due to us trying to acquire a mutex which was never released by another task. Reproducing the exact issue is of course very hard, but this PR aims to make it easier to reason about deadlocks in ApiAvailability by consolidating multiple mutexes into a single one.

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This change is 

[linear]

DES-1263 Daemon stuck in disconnecting state

[dlon]

Reviewed 7 of 7 files at r1, all commit messages.
Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @MarkusPettersson98)

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mullvad-api/src/availability.rs line 163 at r1 (raw file):

        state_ready: impl Fn(State) -> bool,
    ) -> impl Future<Output = Result<(), Error>> {
        let mut rx = self.acquire().tx.subscribe();

What do you think of wrapping this in {} (if clippy is happy with that)? It might just be me but I don't find it obvious that the mutex guard is immediately dropped.

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mullvad-api/src/rest.rs line 187 at r1 (raw file):

    async fn process_command(&mut self, command: RequestCommand) {
        log::debug!("Processing {command:?}");

Should this be removed?

[MarkusPettersson98]

Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @dlon)

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mullvad-api/src/availability.rs line 163 at r1 (raw file):

Previously, dlon (David Lönnhager) wrote…

What do you think of wrapping this in {} (if clippy is happy with that)? It might just be me but I don't find it obvious that the mutex guard is immediately dropped.

That's fine, I don't mind introducing a local scope to make it more obvious that the mutex guard is dropped. I was a bit unsure as well until I looked it up 😊

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mullvad-api/src/rest.rs line 187 at r1 (raw file):

Previously, dlon (David Lönnhager) wrote…

Should this be removed?

Yes! Thanks:)

[dlon]

Reviewed 2 of 2 files at r2, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved