The issue can be reproduced very easily by starting 2 veritysetup processes
at the same time:
$ sudo veritysetup open -v ./img.raw img ./img.verity & sudo veritysetup open -v ./img.raw img ./img.verity
[1] 814021
device-mapper: create ioctl on img CRYPT-VERITY-cea03b7bc5b94e088e5754ff33be71d6-img failed: Device or resource busy
Verity device detected corruption after activation.
Command successful.
Command failed with code -1 (wrong or missing parameters).
Note how veritysetup open is reporting -EINVAL as the return code.
After the fix:
$ sudo veritysetup open -v ./img.raw img ./img.verity & sudo veritysetup open -v ./img.raw img ./img.verity
[1] 814649
Verity device detected corruption after activation.
Command successful.
Device img already exists.
Command failed with code -5 (device already exists or device is busy).
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