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

[Hugh Dickins]

On Mon, 24 Jun 2024, Usama Arif wrote:
> 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@xxxxxxxxx>
> >>> 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.

No doubt you're right (I'm glad I already admitted to being confused).
Personally, I'd just say sizeof(long), but whatever you prefer.

Hugh

> 
> 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;