Re: [PATCH 2/2] arm64: mmu: use pagetable_alloc_nolock() while stop_machine()

Michal Hocko
2025-12-18T09:30:37Z

On Fri 12-12-25 16:18:32, Yeoreum Yun wrote:
> linear_map_split_to_ptes() and __kpti_install_ng_mappings()
> are called as callback of stop_machine().
> That means these functions context are preemption disabled.
>
> Unfortunately, under PREEMPT_RT, the pagetable_alloc() or
> __get_free_pages() couldn't be called in this context
> since spin lock that becomes sleepable on RT,
> potentially causing a sleep during page allocation.
>
> To address this, pagetable_alloc_nolock().

As you cannot tolerate allocation failure and this is pretty much
permanent allocation (AFAIU) why don't you use a static allocation?

--
Michal Hocko
SUSE Labs