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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id d78sm4039758vke.41.2019.06.10.10.26.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Jun 2019 10:26:17 -0700 (PDT) Message-ID: <1560187575.6132.70.camel@lca.pw> Subject: Re: [PATCH -next] arm64/mm: fix a bogus GFP flag in pgd_alloc() From: Qian Cai To: Will Deacon , Mark Rutland Cc: rppt@linux.ibm.com, akpm@linux-foundation.org, catalin.marinas@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 Date: Mon, 10 Jun 2019 13:26:15 -0400 In-Reply-To: <20190610114326.GF15979@fuggles.cambridge.arm.com> References: <1559656836-24940-1-git-send-email-cai@lca.pw> <20190604142338.GC24467@lakrids.cambridge.arm.com> <20190610114326.GF15979@fuggles.cambridge.arm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 2019-06-10 at 12:43 +0100, Will Deacon 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 > > > --- > > >  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()? The offensive commit "arm64: switch to generic version of pte allocation" is not yet in the mainline, but only in the Andrew's tree and linux-next, and I doubt Andrew will push this out any time sooner given it is broken.