Re: [PATCH v2] kasan: remove kasan_find_vm_area() to prevent possible deadlock

[Yeoreum Yun <yeoreum.yun@arm.com>]

Hi Andrey,

> >
> > find_vm_area() couldn't be called in atomic_context.
> > If find_vm_area() is called to reports vm area information,
> > kasan can trigger deadlock like:
> >
> > CPU0                                CPU1
> > vmalloc();
> >  alloc_vmap_area();
> >   spin_lock(&vn->busy.lock)
> >                                     spin_lock_bh(&some_lock);
> >    <interrupt occurs>
> >    <in softirq>
> >    spin_lock(&some_lock);
> >                                     <access invalid address>
> >                                     kasan_report();
> >                                      print_report();
> >                                       print_address_description();
> >                                        kasan_find_vm_area();
> >                                         find_vm_area();
> >                                          spin_lock(&vn->busy.lock) // deadlock!
> >
> > To prevent possible deadlock while kasan reports, remove kasan_find_vm_area().
>
> Can we keep it for when we are in_task()?

We couldn't do. since when kasan_find_vm_area() is called,
the report_lock is grabbed with irq disabled.

Please check discuss with Andrey Ryabinin:
  https://lore.kernel.org/all/4599f645-f79c-4cce-b686-494428bb9e2a@gmail.com/

Thanks

--
Sincerely,
Yeoreum Yun