Re: [linux-next:master] [mm] 0fa2857d23: WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof

[Usama Arif <usamaarif642@gmail.com>]

On 24/06/2024 18:26, Hugh Dickins wrote:
> On Mon, 24 Jun 2024, Usama Arif wrote:
>> On 24/06/2024 15:05, Yosry Ahmed wrote:
>>> On Mon, Jun 24, 2024 at 1:49 AM kernel test robot <oliver.sang@intel.com>
>>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> kernel test robot noticed
>>>> "WARNING:at_mm/page_alloc.c:#__alloc_pages_noprof" on:
>>>>
>>>> commit: 0fa2857d23aa170e5e28d13c467b303b0065aad8 ("mm: store zero pages to
>>>> be swapped out in a bitmap")
>>>> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master
>>> This is coming from WARN_ON_ONCE_GFP(order > MAX_PAGE_ORDER, gfp), and
>>> is triggered by the new bitmap_zalloc() call in the swapon path. For a
>>> sufficiently large swapfile, bitmap_zalloc() (which uses kmalloc()
>>> under the hood) cannot be used to allocate the bitmap.
>>>
>>> Usama, I think we want to use a variant of kvmalloc() here.
> Yes, I hit the same problem with swapon in my testing,
> and had been intending to send a patch.
>
>> Yes, just testing with below diff now. The patch is not in mm-stable yet, so
>> will just send another revision with below diff included. Thanks!
>>
>>
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index 0b8270359bcf..2263f71baa31 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -2643,7 +2643,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *,
>> specialfile)
>>          free_percpu(p->cluster_next_cpu);
>>          p->cluster_next_cpu = NULL;
>>          vfree(swap_map);
>> -       bitmap_free(p->zeromap);
>> +       kvfree(p->zeromap);
> Yes.
>
>>          kvfree(cluster_info);
>>          /* Destroy swap account information */
>>          swap_cgroup_swapoff(p->type);
>> @@ -3170,7 +3170,7 @@ SYSCALL_DEFINE2(swapon, const char __user *,
>> specialfile, int, swap_flags)
>>                  goto bad_swap_unlock_inode;
>>          }
>>
>> -       p->zeromap = bitmap_zalloc(maxpages, GFP_KERNEL);
>> +       p->zeromap = kvzalloc(DIV_ROUND_UP(maxpages, 8), GFP_KERNEL);
> No, 8 is not right for 32-bit kernels. I think you want
> 	p->zeromap = kvzalloc(BITS_TO_LONGS(maxpages), GFP_KERNEL);
> but please check it carefully, I'm easily confused by such conversions.
>
> Hugh

Ah yes, didnt take into account 32-bit kernel. I think its supposed to be

  p->zeromap = kvzalloc(BITS_TO_LONGS(maxpages) * sizeof(unsigned long), 
GFP_KERNEL);

if using BITS_TO_LONGS.

Will wait sometime incase there are more comments and will send out 
another version.

Thanks!

>>          if (!p->zeromap) {
>>                  error = -ENOMEM;
>>                  goto bad_swap_unlock_inode;