On Tue, Jun 04, 2019 at 03:30:20PM +0100, Mark Rutland wrote: > 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@xxxxxx> > > > --- > > > 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. > > I see that since [1], pgd_alloc() was updated to special-case the > init_mm, which is not sufficient for cases like: > > efi_mm.pgd = pgd_alloc(&efi_mm) > > ... which occurs in a kthread. > > So let's have a pgd_alloc_kernel() to make that explicit. I've hit "send" before seeing this one :) Well, to be completely on the safe side an explicit pgd_alloc_kernel() sounds right. Then it won't be subject to future changes in memcg and will always "Do The Right Thing". > Thanks, > Mark. > -- Sincerely yours, Mike.
