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

[Usama Arif]

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.

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;