Xtensa Multi-core critical-section is not sound(?)

[i404788]

I'm currently debugging a weird issue on the ESP32S3 with embassy multi-core related to critical section, as it seems like it tries to double-unlock the MULTICORE_LOCK from different threads when using the embassy executor and I'm not entirely sure why it happens.

What seems to happen:

• esp-hal's embassy impl uses set_alarm for the executor poll (Seems to be on thread_id=1, token=4294967295)
• In set_alarm it aquires a critical_section, and at the end attempts to drop it
• While Dropping (at https://github.com/esp-rs/esp-hal/blob/main/esp-hal/src/lib.rs#L279) a level3 interrupt hits
• The interrupt gets handled by time_driver_timg.rs EmbassyTimer::on_interrupt
• EmbassyTimer::on_interrupt aquires it's own critical_section and when it tries to drop the owner isn't thread_id() (thread_id seems to be 0 at this stack frame).

I'm not sure how it's possible to have 2 threads in one call stack, but it seems like thread_1 unlocks, and before finishing the sync thread_0 locks, causing thread_1 to overwrite the owner. Let me know if I'm missing something

[MabezDev]

@bugadani sorry for the ping, but do you have any ideas on this one?

[bugadani]

Someone broke this assumption

[bjoernQ]

Oh this

fn get_raw_core() -> usize {
    ((xtensa_lx::get_processor_id() as usize & 0x2000) != 0) as usize
}

will very likely produce a value of 1

[MabezDev]

Git blaming that line points me to this PR: #1126 I'm not sure what the crash was? I don't see an issue associated with it.

[bjoernQ]

IIRC there was a discussion in the Matrix channel - ah yes ... there it is: https://matrix.to/#/!LdaNPfUfvefOLewEIM:matrix.org/$LXNqhvjxecSQlJFK-mmJCIYYJ_fgStulDsr5r1mNb-o?via=matrix.org&via=tchncs.de&via=mozilla.org

[MabezDev]

@i404788 Apologies for the breakage, I have the fix in #1175, would you mind giving it a try? Likewise @ProfFan would you mind testing that I haven't broken your use case too?

[ProfFan]

Git blaming that line points me to this PR: #1126 I'm not sure what the crash was? I don't see an issue associated with it.

Oops, it's me :P