Service interruption via synchronous EROFS decompression

Improper atomic-context handling in Linux EROFS before 6.4.7 allows local users to interrupt service through compressed-file reads. The z_erofs_decompressqueue_endio path can run under an RCU read lock, but its context check incorrectly permits synchronous decompression and a sleeping mutex operation instead of handing work to an asynchronous worker. Reachability requires local low-privileged access and activity that exercises compressed EROFS reads; the documented consequence affects availability, with no confidentiality or integrity impact.