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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 5 Jun 2019 22:33:46 +0100 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x55LXjbm54984766 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 5 Jun 2019 21:33:45 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id ABD83A405F; Wed, 5 Jun 2019 21:33:45 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 80203A4054; Wed, 5 Jun 2019 21:33:44 +0000 (GMT) Received: from rapoport-lnx (unknown [9.148.207.19]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTPS; Wed, 5 Jun 2019 21:33:44 +0000 (GMT) Date: Thu, 6 Jun 2019 00:33:42 +0300 From: Mike Rapoport To: Mark Rutland Cc: Qian Cai , 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() References: <1559656836-24940-1-git-send-email-cai@lca.pw> <20190604142338.GC24467@lakrids.cambridge.arm.com> <20190604143020.GD24467@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190604143020.GD24467@lakrids.cambridge.arm.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 19060521-0020-0000-0000-000003469105 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19060521-0021-0000-0000-00002199A1F4 Message-Id: <20190605213342.GA7023@rapoport-lnx> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-05_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=60 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906050136 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 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 > > > --- > > > 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.