Re: [PATCH] powerpc/iommu: Fix an RCU read lock leak in mm_iommu_is_devmem()

[Markus Elfring]

…
> +++ b/arch/powerpc/mm/book3s64/iommu_api.c
> @@ -371,6 +371,7 @@ bool mm_iommu_is_devmem(struct mm_struct *mm, unsigned long hpa,
>  			 * and the caller needs to distinguish this situation.
>  			 */
>  			*size = min(1UL << pageshift, end - hpa);
> +			rcu_read_unlock();
>  			return true;
>  		}
>  	}

Under which circumstances would you become interested to apply a statement
like “guard(rcu)();”?
https://elixir.bootlin.com/linux/v7.3/source/include/linux/rcupdate.h#L1216

Regards,
Markus