[PATCH 29/33] sched/arm64: Move fallback task cpumask to HK_TYPE_DOMAIN

[Will Deacon]

On Sun, Jan 25, 2026 at 11:45:36PM +0100, Frederic Weisbecker wrote:
> When none of the allowed CPUs of a task are online, it gets migrated
> to the fallback cpumask which is all the non nohz_full CPUs.
> 
> However just like nohz_full CPUs, domain isolated CPUs don't want to be
> disturbed by tasks that have lost their CPU affinities.
> 
> And since nohz_full rely on domain isolation to work correctly, the
> housekeeping mask of domain isolated CPUs should always be a subset of
> the housekeeping mask of nohz_full CPUs (there can be CPUs that are
> domain isolated but not nohz_full, OTOH there shouldn't be nohz_full
> CPUs that are not domain isolated):
> 
> 	HK_TYPE_DOMAIN & HK_TYPE_KERNEL_NOISE == HK_TYPE_DOMAIN
> 
> Therefore use HK_TYPE_DOMAIN as the appropriate fallback target for
> tasks. Note that cpuset isolated partitions are not supported on those
> systems and may result in undefined behaviour.
> 
> Signed-off-by: Frederic Weisbecker <frederic at kernel.org>
> Reviewed-by: Waiman Long <longman at redhat.com>
> ---
>  Documentation/arch/arm64/asymmetric-32bit.rst | 12 ++++++++----
>  arch/arm64/kernel/cpufeature.c                |  6 +++---
>  2 files changed, 11 insertions(+), 7 deletions(-)

Thanks, Frederic, this looks much better to me. I also chucked my old
tests at it and it looked good, so:

Acked-by: Will Deacon <will at kernel.org>
Tested-by: Will Deacon <will at kernel.org>

Will