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charset="us-ascii" Content-ID: <841AD1E3E71FE04DAB5DE33BB85DF397@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 40f27527-8065-440d-03d6-08d6ede38ee0 X-MS-Exchange-CrossTenant-originalarrivaltime: 10 Jun 2019 20:38:13.4326 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: guro@fb.com X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN8PR15MB2770 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-10_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 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-1906100139 X-FB-Internal: deliver 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, Jun 10, 2019 at 04:33:44PM -0400, Johannes Weiner wrote: > On Sun, Jun 09, 2019 at 03:10:52PM +0300, Vladimir Davydov wrote: > > On Tue, Jun 04, 2019 at 07:44:45PM -0700, Roman Gushchin wrote: > > > Johannes noticed that reading the memcg kmem_cache pointer in > > > cache_from_memcg_idx() is performed using READ_ONCE() macro, > > > which doesn't implement a SMP barrier, which is required > > > by the logic. > > >=20 > > > Add a proper smp_rmb() to be paired with smp_wmb() in > > > memcg_create_kmem_cache(). > > >=20 > > > The same applies to memcg_create_kmem_cache() itself, > > > which reads the same value without barriers and READ_ONCE(). > > >=20 > > > Suggested-by: Johannes Weiner > > > Signed-off-by: Roman Gushchin > > > --- > > > mm/slab.h | 1 + > > > mm/slab_common.c | 3 ++- > > > 2 files changed, 3 insertions(+), 1 deletion(-) > > >=20 > > > diff --git a/mm/slab.h b/mm/slab.h > > > index 739099af6cbb..1176b61bb8fc 100644 > > > --- a/mm/slab.h > > > +++ b/mm/slab.h > > > @@ -260,6 +260,7 @@ cache_from_memcg_idx(struct kmem_cache *s, int id= x) > > > * memcg_caches issues a write barrier to match this (see > > > * memcg_create_kmem_cache()). > > > */ > > > + smp_rmb(); > > > cachep =3D READ_ONCE(arr->entries[idx]); > >=20 > > Hmm, we used to have lockless_dereference() here, but it was replaced > > with READ_ONCE some time ago. The commit message claims that READ_ONCE > > has an implicit read barrier in it. >=20 > Thanks for catching this Vladimir. I wasn't aware of this change to > the memory model. Indeed, we don't need to change anything here. Cool, I'm dropping this patch. Thanks!