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Fri, 8 Nov 2019 03:58:45 +0000 From: Song Liu To: Andrew Morton CC: open list , "linux-mm@kvack.org" , "matthew.wilcox@oracle.com" , Kernel Team , "william.kucharski@oracle.com" , "kirill.shutemov@linux.intel.com" , "Johannes Weiner" , Hugh Dickins Subject: Re: [PATCH v5 1/2] mm,thp: recheck each page before collapsing file THP Thread-Topic: [PATCH v5 1/2] mm,thp: recheck each page before collapsing file THP Thread-Index: AQHVlGjXjTBN2suIgEyiHRjQ3h6QAaeAp1YAgAABeQA= Date: Fri, 8 Nov 2019 03:58:44 +0000 Message-ID: <47A1A0C0-8E38-4F4E-B7D6-7B390E7F7813@fb.com> References: <20191106060930.2571389-1-songliubraving@fb.com> <20191106060930.2571389-2-songliubraving@fb.com> <20191107195328.600f302bbde69cf9c1089500@linux-foundation.org> In-Reply-To: <20191107195328.600f302bbde69cf9c1089500@linux-foundation.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3601.0.10) x-originating-ip: [2620:10d:c090:180::f533] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 0e47cb15-7849-4258-fbff-08d763fff395 x-ms-traffictypediagnostic: MWHPR15MB1568: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:7691; 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charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 0e47cb15-7849-4258-fbff-08d763fff395 X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Nov 2019 03:58:44.9018 (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: GLd68GMyul+JhkEr94Tp2L/wCAB5P3CBqcRe/LO8S0774tkUXWvG9nXT9QEJxN5hq0vlbs2GyYdYJ++a3bByFw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1568 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-11-07_07:2019-11-07,2019-11-07 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 clxscore=1015 phishscore=0 mlxscore=0 bulkscore=0 malwarescore=0 impostorscore=0 adultscore=0 priorityscore=1501 suspectscore=0 spamscore=0 mlxlogscore=999 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1911080037 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 Nov 7, 2019, at 7:53 PM, Andrew Morton wro= te: >=20 > On Tue, 5 Nov 2019 22:09:29 -0800 Song Liu wrote: >=20 >> In collapse_file(), for !is_shmem case, current check cannot guarantee >> the locked page is up-to-date. Specifically, xas_unlock_irq() should >> not be called before lock_page() and get_page(); and it is necessary to >> recheck PageUptodate() after locking the page. >>=20 >> With this bug and CONFIG_READ_ONLY_THP_FOR_FS=3Dy, madvise(HUGE)'ed .tex= t >> may contain corrupted data. This is because khugepaged mistakenly >> collapses some not up-to-date sub pages into a huge page, and assumes >> the huge page is up-to-date. This will NOT corrupt data in the disk, >> because the page is read-only and never written back. Fix this by >> properly checking PageUptodate() after locking the page. This check >> replaces "VM_BUG_ON_PAGE(!PageUptodate(page), page);". >>=20 >> Also, move PageDirty() check after locking the page. Current >> khugepaged should not try to collapse dirty file THP, because it is >> limited to read-only .text. The only case we hit a dirty page here is >> when the page hasn't been written since write. Bail out and retry when >> this happens. >=20 > Incorrect data is pretty serious. Should we backport this into -stable > kernels? >=20 > (I suspect I already asked this in response to earier versions, sorry ;)) This is new feature (and new bug :( ) in 5.4. So no need to back port. Thanks, Song=