linuxkpi: Allow ida_destroy and idr_destroy to be called multiple times

[ashafer_badland.io]

Summary

This fixes some weird behavior triggered by nvidia-drm.ko: some DRM
cleanup functions will be called multiple times, leading to a double
free. drm_mode_config_cleanup will be called twice, causing ida_destroy
to be called twice. Although calling the cleanup twice doesn't seem
very clean, on Linux this seems to be permissable as it handles it
just fine.

In order to preserve this behavior this change checks if the objects
have already been destroyed and bails if so. This fixes the panic seen
when unloading the nvidia-drm driver.

[bz]

Nice tracking down.
Is there a PR for this somewhere we need to reference?

Are you actually seeing a double-free as indicated in the description or is the panic on acquiring a non-initilized mutex?

sys/compat/linuxkpi/common/src/linux_idr.c

182

"If" upper case and I'd remove the "empty/" as we don't check for that.

184

I think this should be part of the commit message.
I'd rather state that the idr can be re-used--only freeing the internal memory--and we could be called multiple times without an idr_init() in between so guarding for that.

188

You wouldn't need the { } and a space after if.

I do wonder if there is any other pointer or simple data type we could check here instead of whether the mutex is initialized? Likely not easily ... given the mtx_destroy(). Hmm. Guess not.

[ashafer_badland.io]

There isn't a PR, this has been a longstanding issue with nvidia-drm that I'm
finally getting around to solving.

If you unload nvidia-drm.ko right now you'll see a panic from the mutex
initialization assert. If you fix that (idr_destroy part of this change) then
you'll run into a double free (ida_destroy part of this change).

[bz]

Thanks. If no one complains the next days I'll put this in.

[manu]

sys/compat/linuxkpi/common/src/linux_idr.c

186

mtx_initialized returns an int so style(9) says to not use ! but == 0

[ashafer_badland.io]

Updated with style, thanks.

[ashafer_badland.io]

Any update on getting this merged?