Re: [PATCH] kasan: Don't call find_vm_area() in RT kernel

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

On Tue, Feb 11, 2025 at 5:08 PM Waiman Long <longman@redhat.com> wrote:
> diff --git a/mm/kasan/report.c b/mm/kasan/report.c
> index 3fe77a360f1c..e1ee687966aa 100644
> --- a/mm/kasan/report.c
> +++ b/mm/kasan/report.c
> @@ -398,9 +398,20 @@ static void print_address_description(void *addr, u8 tag,
>                 pr_err("\n");
>         }
>
> -       if (is_vmalloc_addr(addr)) {
> -               struct vm_struct *va = find_vm_area(addr);
> +       if (!is_vmalloc_addr(addr))
> +               goto print_page;
>
> +       /*
> +        * RT kernel cannot call find_vm_area() in atomic context.
> +        * For !RT kernel, prevent spinlock_t inside raw_spinlock_t warning
> +        * by raising wait-type to WAIT_SLEEP.
> +        */
> +       if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
> +               static DEFINE_WAIT_OVERRIDE_MAP(vmalloc_map, LD_WAIT_SLEEP);
> +               struct vm_struct *va;
> +
> +               lock_map_acquire_try(&vmalloc_map);
> +               va = find_vm_area(addr);

Can we hide all this logic behind some function like
kasan_find_vm_area() which would return NULL for -rt?

>                 if (va) {
>                         pr_err("The buggy address belongs to the virtual mapping at\n"
>                                " [%px, %px) created by:\n"
> @@ -410,8 +421,13 @@ static void print_address_description(void *addr, u8 tag,
>
>                         page = vmalloc_to_page(addr);

Or does vmalloc_to_page() secretly take  some lock somewhere so we
need to guard it with this 'vmalloc_map' too?
So my suggestion above wouldn't be enough, if that's the case.

>                 }
> +               lock_map_release(&vmalloc_map);
> +       } else {
> +               pr_err("The buggy address %px belongs to a vmalloc virtual mapping\n",
> +                       addr);
>         }
>