From: Mike Rapoport <rppt@linux.ibm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Qian Cai <cai@lca.pw>,
akpm@linux-foundation.org, catalin.marinas@arm.com,
will.deacon@arm.com, linux-kernel@vger.kernel.org,
mhocko@kernel.org, linux-mm@kvack.org, vdavydov.dev@gmail.com,
hannes@cmpxchg.org, cgroups@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd_alloc()
Date: Thu, 6 Jun 2019 00:33:42 +0300 [thread overview]
Message-ID: <20190605213342.GA7023@rapoport-lnx> (raw)
In-Reply-To: <20190604143020.GD24467@lakrids.cambridge.arm.com>
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@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.
>
> 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.
next prev parent reply other threads:[~2019-06-05 21:33 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-04 14:00 [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd_alloc() Qian Cai
2019-06-04 14:23 ` Mark Rutland
2019-06-04 14:30 ` Mark Rutland
2019-06-05 21:33 ` Mike Rapoport [this message]
2019-06-04 14:54 ` Mike Rapoport
2019-06-10 11:43 ` Will Deacon
2019-06-10 17:26 ` Qian Cai
2019-06-11 10:03 ` Mark Rutland
2019-06-11 12:41 ` Mike Rapoport
2019-06-11 12:46 ` Qian Cai
2019-06-12 6:57 ` Mike Rapoport
2019-06-12 18:35 ` Qian Cai
2019-06-11 13:02 ` Mark Rutland
2019-06-13 12:11 ` Mike Rapoport
2019-06-13 13:22 ` Qian Cai
2019-06-13 19:44 ` Mike Rapoport
2019-06-17 15:12 ` Mike Rapoport
2019-06-17 16:36 ` Will Deacon
2019-06-18 6:12 ` Mike Rapoport
2019-06-18 6:54 ` Will Deacon
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