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

[Hugh Dickins <hughd@google.com>]

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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

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