Jesper Dangaard Brouer <brouer@xxxxxxxxxx> writes: > On Wed, 15 Apr 2020 16:01:51 +0200 > Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote: > >> When the kernel is built with CONFIG_DEBUG_PER_CPU_MAPS, the cpumap code >> can trigger a spurious warning if CONFIG_CPUMASK_OFFSTACK is also set. This >> happens because in this configuration, NR_CPUS can be larger than >> nr_cpumask_bits, so the initial check in cpu_map_alloc() is not sufficient >> to guard against hitting the warning in cpumask_check(). >> >> Fix this by using the nr_cpumask_bits variable in the map creation code >> instead of the NR_CPUS constant. > > Shouldn't you use 'nr_cpu_ids' instead of 'nr_cpumask_bits' ? > > Else this will still fail on systems with CONFIG_CPUMASK_OFFSTACK=n. Jesper and I had an offlist discussion about this, and decided that it's actually better to keep the check in cpu_map_alloc as-is, and instead just check against nr_cpumask_bits in cpu_map_update_elem(). Otherwise, the max-size of the map can vary between machines which can affect BPF program portability. I'll send a v2. -Toke
