On Fri, Jun 02, 2017 at 09:28:56AM +0200, Michal Hocko wrote:
> On Fri 02-06-17 07:17:22, Sasha Levin wrote:
> > On Mon, Mar 06, 2017 at 11:30:24AM +0100, Michal Hocko wrote:
> > > +void *kvmalloc_node(size_t size, gfp_t flags, int node)
> > > +{
> > > + gfp_t kmalloc_flags = flags;
> > > + void *ret;
> > > +
> > > + /*
> > > + * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
> > > + * so the given set of flags has to be compatible.
> > > + */
> > > + WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
> >
> > Hm, there are quite a few locations in the kernel that do something like:
> >
> > __vmalloc(len, GFP_NOFS, PAGE_KERNEL);
> >
> > According to your patch, vmalloc can't really do GFP_NOFS, right?
>
> Yes. It is quite likely that they will just work because the hardcoded
> GFP_KERNEL inside the vmalloc path is in unlikely paths (page table
> allocations for example) but yes they are broken. I didn't convert some
> places which opencode the kvmalloc with GFP_NOFS because I strongly
> _believe_ that the GFP_NOFS should be revisited, checked whether it is
> needed, documented if so and then memalloc_nofs__{save,restore} be used
> for the scope which is reclaim recursion unsafe. This would turn all
> those vmalloc users to the default GFP_KERNEL and still do the right
> thing.
While you haven't converted those paths, other folks have picked up
on that:
commit beeeccca9bebcec386cc31c250cff8a06cf27034
Author: Vinnie Magro <vmagro@xxxxxx>
Date: Thu May 25 12:18:02 2017 -0700
btrfs: Use kvzalloc instead of kzalloc/vmalloc in alloc_bitmap
[...]
Maybe we should make kvmalloc_node() fail non-GFP_KERNEL allocations
rather than just warn on them to make this error more evident? I'm not
sure how these warnings were missed during testing.
--
Thanks,
Sasha
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