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Sun, 8 Apr 2018 20:42:23 -0400 From: Sasha Levin To: "stable@vger.kernel.org" , "linux-kernel@vger.kernel.org" CC: Mel Gorman , "Huang, Ying" , Jan Kara , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH AUTOSEL for 3.18 087/101] mm: pin address_space before dereferencing it while isolating an LRU page Thread-Topic: [PATCH AUTOSEL for 3.18 087/101] mm: pin address_space before dereferencing it while isolating an LRU page Thread-Index: AQHTz5uJsdBMIypNnkG5a/xYaPMJsQ== Date: Mon, 9 Apr 2018 00:41:45 +0000 Message-ID: <20180409004042.164920-37-alexander.levin@microsoft.com> References: <20180409004042.164920-1-alexander.levin@microsoft.com> In-Reply-To: <20180409004042.164920-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR2101MB1062;7:ejnF/sJnf5EW1bYhVqfTHR6+IlL8KT9AL3e5WCreKEH5a08V7a014E4qmn/gNgZqaB/N+tD/w1ZvvXCisS8UQkEgOI+8NddKpehtJ557DplZ8XL9n2ih6g7YzYYAyUXQMw4k4ZVTSFXvGAqZnO1t/geHxgHQXROXacPFvkeT2Rc9SBLyHF+vQhR2SVVa7SzuBWhfqM4GnYZz46C7X3bQ1jIQtV1bSR15u34/v8ocR0b47JCDSssRix5OLPHhlyGc;20:yxWCBhpOsxAGVSrHnZZYP4v0PG5B7/Hu9PoROF83ZmNfIqFB/jIrEP3lpuzEpWbAeMPy8FoE7TAdW482GkmEuBZl2BsoYLxOaYLPHTIej0lvWvovDsrv4v4y+aHFxZc+6dqa4cPd5u1FzUakc/gjY+CiPux5z/l9VFvLmzDpv/4= x-ms-office365-filtering-ht: Tenant X-MS-Office365-Filtering-Correlation-Id: 3b9ac946-2ec4-474b-d789-08d59db2be57 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB1062; 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x-microsoft-antispam-message-info: 4qC7nXO9OA3AJwroZWp1/lT1uw4K96GOfldYgk8fEAqsLEf6ISIzj2FwANs/Q7iABPHSvajGOciqgPqcyVDdMM+V445EKUlS7xbrYRYD1Q3LZEw3miLdeloi2ZKkJd0kyrLGr1Ben07uI8prxSkaHQvVzt4oiHBNxbgD4O8zoI833zWtDpKar2LxYad5AIGVmqNY7L3TCqEsLFlVSHEx2WqYY/9nn+rRvuEqtA5aBtFNjYvYnNzCCkrv1H+p5YySS9jZLcEPctxj2AmFJdGtuVaIZIMpBwVU8k4MYl8gOCuOBWvHSWFui1aaXSv3smobPdsQf+rHGk84aEBStyHxBK61V0bGC/va4GbIHVUKsLB8Yrc0/3qBWV97J5wPpCB39Xa6dUM80VtpcrUHyWBPmiwRzfbviE8JO+OPbsMjQuI= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3b9ac946-2ec4-474b-d789-08d59db2be57 X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Apr 2018 00:41:45.6741 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB1062 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Mel Gorman [ Upstream commit 69d763fc6d3aee787a3e8c8c35092b4f4960fa5d ] Minchan Kim asked the following question -- what locks protects address_space destroying when race happens between inode trauncation and __isolate_lru_page? Jan Kara clarified by describing the race as follows CPU1 CPU2 truncate(inode) __isolate_lru_page() ... truncate_inode_page(mapping, page); delete_from_page_cache(page) spin_lock_irqsave(&mapping->tree_lock, flags); __delete_from_page_cache(page, NULL) page_cache_tree_delete(..) ... mapping =3D page_mapping(= page); page->mapping =3D NULL; ... spin_unlock_irqrestore(&mapping->tree_lock, flags); page_cache_free_page(mapping, page) put_page(page) if (put_page_testzero(page)) -> false - inode now has no pages and can be freed including embedded address_space if (mapping && !mapping->= a_ops->migratepage) - we've dereferenced mapping which is potentially already free. The race is theoretically possible but unlikely. Before the delete_from_page_cache, truncate_cleanup_page is called so the page is likely to be !PageDirty or PageWriteback which gets skipped by the only caller that checks the mappping in __isolate_lru_page. Even if the race occurs, a substantial amount of work has to happen during a tiny window with no preemption but it could potentially be done using a virtual machine to artifically slow one CPU or halt it during the critical window. This patch should eliminate the race with truncation by try-locking the page before derefencing mapping and aborting if the lock was not acquired. There was a suggestion from Huang Ying to use RCU as a side-effect to prevent mapping being freed. However, I do not like the solution as it's an unconventional means of preserving a mapping and it's not a context where rcu_read_lock is obviously protecting rcu data. Link: http://lkml.kernel.org/r/20180104102512.2qos3h5vqzeisrek@techsingular= ity.net Fixes: c82449352854 ("mm: compaction: make isolate_lru_page() filter-aware = again") Signed-off-by: Mel Gorman Acked-by: Minchan Kim Cc: "Huang, Ying" Cc: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/vmscan.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 6d652990433a..9d38cf604760 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1215,6 +1215,7 @@ int __isolate_lru_page(struct page *page, isolate_mod= e_t mode) =20 if (PageDirty(page)) { struct address_space *mapping; + bool migrate_dirty; =20 /* ISOLATE_CLEAN means only clean pages */ if (mode & ISOLATE_CLEAN) @@ -1223,10 +1224,19 @@ int __isolate_lru_page(struct page *page, isolate_m= ode_t mode) /* * Only pages without mappings or that have a * ->migratepage callback are possible to migrate - * without blocking + * without blocking. However, we can be racing with + * truncation so it's necessary to lock the page + * to stabilise the mapping as truncation holds + * the page lock until after the page is removed + * from the page cache. */ + if (!trylock_page(page)) + return ret; + mapping =3D page_mapping(page); - if (mapping && !mapping->a_ops->migratepage) + migrate_dirty =3D mapping && mapping->a_ops->migratepage; + unlock_page(page); + if (!migrate_dirty) return ret; } } --=20 2.15.1