Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752599AbdDJCXU (ORCPT ); Sun, 9 Apr 2017 22:23:20 -0400 Received: from omzsmtpe02.verizonbusiness.com ([199.249.25.209]:14166 "EHLO omzsmtpe02.verizonbusiness.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751209AbdDJCXS (ORCPT ); Sun, 9 Apr 2017 22:23:18 -0400 X-IronPort-Anti-Spam-Filtered: false X-IronPort-AV: E=Sophos;i="5.37,180,1488844800"; d="scan'208";a="329605757" From: alexander.levin@verizon.com X-Host: ranger.odc.vzwcorp.com To: Johannes Weiner CC: Andrew Morton , Tejun Heo , Hugh Dickins , Michel Lespinasse , "Jan Kara" , "Kirill A. Shutemov" , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [patch 1/3] mm: protect set_page_dirty() from ongoing truncation Thread-Topic: [patch 1/3] mm: protect set_page_dirty() from ongoing truncation Thread-Index: AQHSsaFPuuVOhWwayEyi5lQohLkOPg== Date: Mon, 10 Apr 2017 02:22:33 +0000 Message-ID: <20170410022230.xe5sukvflvoh4ula@sasha-lappy> References: <1417791166-32226-1-git-send-email-hannes@cmpxchg.org> In-Reply-To: <1417791166-32226-1-git-send-email-hannes@cmpxchg.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Mutt/1.6.2-neo (2016-08-21) x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.144.60.250] Content-Type: text/plain; charset="us-ascii" Content-ID: <33D4FD5514C5E9408FA87A7A3A9773CB@vzwcorp.com> MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id v3A2NOjC023419 Content-Length: 7738 Lines: 101 On Fri, Dec 05, 2014 at 09:52:44AM -0500, Johannes Weiner wrote: > Tejun, while reviewing the code, spotted the following race condition > between the dirtying and truncation of a page: > > __set_page_dirty_nobuffers() __delete_from_page_cache() > if (TestSetPageDirty(page)) > page->mapping = NULL > if (PageDirty()) > dec_zone_page_state(page, NR_FILE_DIRTY); > dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); > if (page->mapping) > account_page_dirtied(page) > __inc_zone_page_state(page, NR_FILE_DIRTY); > __inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE); > > which results in an imbalance of NR_FILE_DIRTY and BDI_RECLAIMABLE. > > Dirtiers usually lock out truncation, either by holding the page lock > directly, or in case of zap_pte_range(), by pinning the mapcount with > the page table lock held. The notable exception to this rule, though, > is do_wp_page(), for which this race exists. However, do_wp_page() > already waits for a locked page to unlock before setting the dirty > bit, in order to prevent a race where clear_page_dirty() misses the > page bit in the presence of dirty ptes. Upgrade that wait to a fully > locked set_page_dirty() to also cover the situation explained above. > > Afterwards, the code in set_page_dirty() dealing with a truncation > race is no longer needed. Remove it. > > Reported-by: Tejun Heo > Signed-off-by: Johannes Weiner > Cc: > Acked-by: Kirill A. Shutemov Hi Johannes, I'm seeing the following while fuzzing with trinity on linux-next (I've changed the WARN to a VM_BUG_ON_PAGE for some extra page info). [ 18.991007] page:ffffea000307c8c0 count:3 mapcount:0 mapping:ffff88010444cbf8 index:0x1^M [ 18.993051] flags: 0x1fffc0000000011(locked|dirty)^M [ 18.993621] raw: 01fffc0000000011 ffff88010444cbf8 0000000000000001 00000003ffffffff^M [ 18.994522] raw: dead000000000100 dead000000000200 0000000000000000 ffff880109c38008^M [ 18.995418] page dumped because: VM_BUG_ON_PAGE(!PagePrivate(page) && !PageUptodate(page))^M [ 18.996381] page->mem_cgroup:ffff880109c38008^M [ 18.996935] ------------[ cut here ]------------^M [ 18.997483] kernel BUG at mm/page-writeback.c:2486!^M [ 18.998063] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN^M [ 18.998756] Modules linked in:^M [ 18.999129] CPU: 5 PID: 1388 Comm: trinity-c34 Not tainted 4.11.0-rc5-next-20170407-dirty #12^M [ 19.000117] task: ffff880106ee5d40 task.stack: ffff8800c0f40000^M [ 19.000828] RIP: 0010:__set_page_dirty_nobuffers (??:?) [ 19.001491] RSP: 0018:ffff8800c0f47318 EFLAGS: 00010006^M [ 19.002103] RAX: 0000000000000000 RBX: 1ffff100181e8e67 RCX: 0000000000000000^M [ 19.002929] RDX: 0000000000000021 RSI: 1ffff100181e8da7 RDI: ffffed00181e8e58^M [ 19.004806] RBP: ffff8800c0f47440 R08: 3830303833633930 R09: 3130383866666666^M [ 19.005626] R10: dffffc0000000000 R11: 0000000000001491 R12: ffff8800c0f47418^M [ 19.006452] R13: ffffea000307c8c0 R14: ffff88010444cc10 R15: ffff88010444cbf8^M [ 19.007277] FS: 00007ff6a26fb700(0000) GS:ffff88010a340000(0000) knlGS:0000000000000000^M [ 19.008424] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033^M [ 19.009092] CR2: 00007ff6a155267c CR3: 00000000cb301000 CR4: 00000000000406a0^M [ 19.009919] Call Trace:^M [ 19.012266] set_page_dirty (mm/page-writeback.c:2579) [ 19.020028] v9fs_write_end (fs/9p/vfs_addr.c:325) [ 19.022473] generic_perform_write (mm/filemap.c:2842) [ 19.024857] __generic_file_write_iter (mm/filemap.c:2957) [ 19.025830] generic_file_write_iter (./include/linux/fs.h:702 mm/filemap.c:2985) [ 19.028549] __do_readv_writev (./include/linux/fs.h:1734 fs/read_write.c:696 fs/read_write.c:862) [ 19.029924] do_readv_writev (fs/read_write.c:895) [ 19.034044] vfs_writev (fs/read_write.c:921) [ 19.035223] do_writev (fs/read_write.c:955) [ 19.036925] SyS_writev (fs/read_write.c:1024) [ 19.037297] do_syscall_64 (arch/x86/entry/common.c:284) [ 19.042085] entry_SYSCALL64_slow_path (arch/x86/entry/entry_64.S:249) [ 19.042608] RIP: 0033:0x7ff6a200a8e9^M [ 19.043015] RSP: 002b:00007fff78079608 EFLAGS: 00000246 ORIG_RAX: 0000000000000014^M [ 19.044253] RAX: ffffffffffffffda RBX: 0000000000000014 RCX: 00007ff6a200a8e9^M [ 19.045045] RDX: 0000000000000001 RSI: 0000000002337d60 RDI: 000000000000018b^M [ 19.045835] RBP: 00007ff6a2601000 R08: 000000482a1a83cf R09: fffdffffffffffff^M [ 19.046627] R10: 0012536735f82cf7 R11: 0000000000000246 R12: 0000000000000002^M [ 19.047413] R13: 00007ff6a2601048 R14: 00007ff6a26fb698 R15: 00007ff6a2601000^M [ 19.048212] Code: 89 85 f0 fe ff ff e8 39 1b 20 00 8b 85 f0 fe ff ff eb 1a e8 2c bd 12 00 31 c0 eb 11 48 c7 c6 e0 c4 47 83 4c 89 ef e8 39 44 07 00 <0f> 0b 48 ba 00 00 00 00 00 fc ff df 48 c7 04 13 00 00 00 00 48 ^M All code ======== 0: 89 85 f0 fe ff ff mov %eax,-0x110(%rbp) 6: e8 39 1b 20 00 callq 0x201b44 b: 8b 85 f0 fe ff ff mov -0x110(%rbp),%eax 11: eb 1a jmp 0x2d 13: e8 2c bd 12 00 callq 0x12bd44 18: 31 c0 xor %eax,%eax 1a: eb 11 jmp 0x2d 1c: 48 c7 c6 e0 c4 47 83 mov $0xffffffff8347c4e0,%rsi 23: 4c 89 ef mov %r13,%rdi 26: e8 39 44 07 00 callq 0x74464 2b:* 0f 0b ud2 <-- trapping instruction 2d: 48 ba 00 00 00 00 00 movabs $0xdffffc0000000000,%rdx 34: fc ff df 37: 48 c7 04 13 00 00 00 movq $0x0,(%rbx,%rdx,1) 3e: 00 3f: 48 rex.W ... Code starting with the faulting instruction =========================================== 0: 0f 0b ud2 2: 48 ba 00 00 00 00 00 movabs $0xdffffc0000000000,%rdx 9: fc ff df c: 48 c7 04 13 00 00 00 movq $0x0,(%rbx,%rdx,1) 13: 00 14: 48 rex.W ... [ 19.050311] RIP: __set_page_dirty_nobuffers+0x407/0x450 RSP: ffff8800c0f47318^M (??:?) -- Thanks, Sasha