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

[Waiman Long]

On 2/12/25 6:59 AM, Andrey Ryabinin wrote:
> On Tue, Feb 11, 2025 at 5:08 PM Waiman Long <longman@xxxxxxxxxx> 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?
Sure. We can certainly do that.
> >                  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.

AFAICS, vmalloc_to_page() doesn't seem to take any lock.  Even if it 
takes another spinlock, it will still be under the vmalloc_map 
protection until lock_map_release() is called.

Cheers,
Longman