CVE-2026-80963

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

dm-stats: fix a crash if allocation of per-cpu data fails

If "dm_kvzalloc(percpu_alloc_size, cpu_to_node(cpu))" fails, the code
jumps to the "out" label and calls dm_stat_free. dm_stat_free does
"for_each_possible_cpu(cpu) { dm_kvfree(s->stat_percpu[cpu][0].histogram,
s->histogram_alloc_size);", which crashes with NULL pointer dereference
if s->stat_percpu[cpu] is NULL.

This commit fixes the bug by testing s->stat_percpu[cpu] for NULL before
using it.