[PATCH v6 05/14] mm: clarify lazy_mmu sleeping constraints

[David Hildenbrand (Red Hat)]

On 12/15/25 16:03, Kevin Brodsky wrote:
> The lazy MMU mode documentation makes clear that an implementation
> should not assume that preemption is disabled or any lock is held
> upon entry to the mode; however it says nothing about what code
> using the lazy MMU interface should expect.
> 
> In practice sleeping is forbidden (for generic code) while the lazy
> MMU mode is active: say it explicitly.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky at arm.com>
> ---
>   include/linux/pgtable.h | 14 +++++++++-----
>   1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 652f287c1ef6..1abc4a1c3d72 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -225,11 +225,15 @@ static inline int pmd_dirty(pmd_t pmd)
>    * up to date.
>    *
>    * In the general case, no lock is guaranteed to be held between entry and exit
> - * of the lazy mode. So the implementation must assume preemption may be enabled
> - * and cpu migration is possible; it must take steps to be robust against this.
> - * (In practice, for user PTE updates, the appropriate page table lock(s) are
> - * held, but for kernel PTE updates, no lock is held). Nesting is not permitted
> - * and the mode cannot be used in interrupt context.
> + * of the lazy mode. (In practice, for user PTE updates, the appropriate page
> + * table lock(s) are held, but for kernel PTE updates, no lock is held).
> + * The implementation must therefore assume preemption may be enabled upon
> + * entry to the mode and cpu migration is possible; it must take steps to be
> + * robust against this. An implementation may handle this by disabling
> + * preemption, as a consequence generic code may not sleep while the lazy MMU
> + * mode is active.
> + *
> + * Nesting is not permitted and the mode cannot be used in interrupt context.
>    */
>   #ifndef __HAVE_ARCH_ENTER_LAZY_MMU_MODE
>   static inline void arch_enter_lazy_mmu_mode(void) {}

Acked-by: David Hildenbrand (Red Hat) <david at kernel.org>

-- 
Cheers

David