CVE-2026-72223: nvdimm/btt: Free arena sub-allocations on discover_arenas() error path

In the Linux kernel, the following vulnerability has been resolved:

nvdimm/btt: Free arena sub-allocations on discoverarenas() error path

Memory allocated by bttfreelistinit(), bttrttinit(), and bttmaplocksinit() is not freed on some discoverarenas() error paths. This leaks memory when arena discovery fails.

Add the missing kfree() calls to release the allocations before returning an error.

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