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

[Waiman Long <llong@redhat.com>]

On 2/12/25 6:59 AM, Andrey Ryabinin wrote:
> 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?
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