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Sun, 8 Apr 2018 20:24:50 -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 4.14 104/161] mm: pin address_space before dereferencing it while isolating an LRU page Thread-Topic: [PATCH AUTOSEL for 4.14 104/161] mm: pin address_space before dereferencing it while isolating an LRU page Thread-Index: AQHTz5itkDLTllA0qU+lwlqvfrqahw== Date: Mon, 9 Apr 2018 00:21:17 +0000 Message-ID: <20180409001936.162706-104-alexander.levin@microsoft.com> References: <20180409001936.162706-1-alexander.levin@microsoft.com> In-Reply-To: <20180409001936.162706-1-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;DM5PR2101MB0983;7:yudqWVuPOapyffXTJnR0I6i3ffop99HOSMr1R7FpqujUJhC001OhL0lQQsvcHpAUScrB4j6GqfxSP1RnZPckittiTqClR2nOnOlndazwibvDl3oerRdu7qB+hC9CSdVSlgbmTxvGXvynNdI2RHt67zskQdBU4ugfxmWNSGDWlTH41M+uT47Zz6+8brlz99XsVsX4CycG7pBqH7Xa/gQItiDZV6pTP6ku6//pHyq41hwRE5fYBrmbeeVezQO4lDgb;20:kMDntM0qUbBisGbIFIy08c2evjqs84SN2/PJPoMfwV4zkBAAqobErNxpn8grOXWbO/WpGuoJ8DR3YbGU56BPM1GBXXxXI8fC4QWlIiWdhSy71CTSDaYhQWIPFOpk16Vi26K2hv38DYt4ydcElXZ88zL0+2ImD7V77KikXPPeojc= x-ms-office365-filtering-ht: Tenant X-MS-Office365-Filtering-Correlation-Id: fb841f74-4e17-4676-21b6-08d59db04b6a x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB0983; 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x-microsoft-antispam-message-info: fzdgTkfFcuFsnURLgClHDKqwxc3FeGzIVFjVHFOuz+QWbogofSkqV5aWFByyhs/WQYKY/E2NR6LPYoEuzhW8cDw9jY9/xt6FimYUMAblK0bywghLELTlcgcEUQHbCzRkKCW4bk595e9YEjqUli1SZNVAUkIyFT6tEmr/h6hONEet9ikAR3FyJMyH2+aYYlXUvn7BMeDpUwF6eWvYqcoz3agISxcKDCcIwFNF4V/nRNHcyiPdcOmcFejIGw9zWjmRiblxxTITFlL5NGADIG2Z0OoV1TIDSoNp8JRrG01E2ss/4qIezsvD3VDhtGNpZt1GS/sDnd6ALOe39EOxacrP7z2TaAU8colwqpag8gvxYnBGbR2C2XQcxrkoH6NyCm1NM9glc5WHzhwWZRkoGK6VAfqRfK4d8835qtjUcjdwI0s= 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: fb841f74-4e17-4676-21b6-08d59db04b6a X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Apr 2018 00:21:17.4406 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB0983 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 a8a3729bfaa9..b3f5e337b64a 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1436,14 +1436,24 @@ int __isolate_lru_page(struct page *page, isolate_m= ode_t mode) =20 if (PageDirty(page)) { struct address_space *mapping; + bool migrate_dirty; =20 /* * 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