Re: [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd_alloc()

Will Deacon
2019-06-10T11:43:26Z

On Tue, Jun 04, 2019 at 03:23:38PM +0100, Mark Rutland wrote:
> On Tue, Jun 04, 2019 at 10:00:36AM -0400, Qian Cai wrote:
> > The commit "arm64: switch to generic version of pte allocation"
> > introduced endless failures during boot like,
> >
> > kobject_add_internal failed for pgd_cache(285:chronyd.service) (error:
> > -2 parent: cgroup)
> >
> > It turns out __GFP_ACCOUNT is passed to kernel page table allocations
> > and then later memcg finds out those don't belong to any cgroup.
>
> Mike, I understood from [1] that this wasn't expected to be a problem,
> as the accounting should bypass kernel threads.
>
> Was that assumption wrong, or is something different happening here?
>
> >
> > backtrace:
> > kobject_add_internal
> > kobject_init_and_add
> > sysfs_slab_add+0x1a8
> > __kmem_cache_create
> > create_cache
> > memcg_create_kmem_cache
> > memcg_kmem_cache_create_func
> > process_one_work
> > worker_thread
> > kthread
> >
> > Signed-off-by: Qian Cai <cai@lca.pw>
> > ---
> > arch/arm64/mm/pgd.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> > index 769516cb6677..53c48f5c8765 100644
> > --- a/arch/arm64/mm/pgd.c
> > +++ b/arch/arm64/mm/pgd.c
> > @@ -38,7 +38,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
> > if (PGD_SIZE == PAGE_SIZE)
> > return (pgd_t *)__get_free_page(gfp);
> > else
> > - return kmem_cache_alloc(pgd_cache, gfp);
> > + return kmem_cache_alloc(pgd_cache, GFP_PGTABLE_KERNEL);
>
> This is used to allocate PGDs for both user and kernel pagetables (e.g.
> for the efi runtime services), so while this may fix the regression, I'm
> not sure it's the right fix.
>
> Do we need a separate pgd_alloc_kernel()?

So can I take the above for -rc5, or is somebody else working on a different
fix to implement pgd_alloc_kernel()?

/confused

Will