Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754986AbaKSNi0 (ORCPT ); Wed, 19 Nov 2014 08:38:26 -0500 Received: from cantor2.suse.de ([195.135.220.15]:55979 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751968AbaKSNiZ (ORCPT ); Wed, 19 Nov 2014 08:38:25 -0500 Message-ID: <546C9D4D.9090201@suse.cz> Date: Wed, 19 Nov 2014 14:38:21 +0100 From: Vlastimil Babka User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Andrew Morton , Sasha Levin CC: Hugh Dickins , "linux-mm@kvack.org" , LKML , Dave Jones , Jens Axboe Subject: Re: mm: shmem: freeing mlocked page References: <545C4A36.9050702@oracle.com> <5466142C.60100@oracle.com> <20141118135843.bd711e95d3977c74cf51d803@linux-foundation.org> In-Reply-To: <20141118135843.bd711e95d3977c74cf51d803@linux-foundation.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/18/2014 10:58 PM, Andrew Morton wrote: > On Fri, 14 Nov 2014 09:39:40 -0500 Sasha Levin wrote: > >> >> [ 1026.988043] BUG: Bad page state in process trinity-c374 pfn:23f70 >> [ 1026.989684] page:ffffea0000b3d300 count:0 mapcount:0 mapping: (null) index:0x5b >> [ 1026.991151] flags: 0x1fffff8028000c(referenced|uptodate|swapbacked|mlocked) >> [ 1026.992410] page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set >> [ 1026.993479] bad because of flags: >> [ 1026.994125] flags: 0x200000(mlocked) > > Gee that new page dumping code is nice! > >> [ 1026.994816] Modules linked in: >> [ 1026.995378] CPU: 7 PID: 7879 Comm: trinity-c374 Not tainted 3.18.0-rc4-next-20141113-sasha-00047-gd1763ce-dirty #1455 >> [ 1026.996123] FAULT_INJECTION: forcing a failure. >> [ 1026.996123] name failslab, interval 100, probability 30, space 0, times -1 >> [ 1026.999050] 0000000000000000 0000000000000000 0000000000b3d300 ffff88061295bbd8 >> [ 1027.000676] ffffffff92f71097 0000000000000000 ffffea0000b3d300 ffff88061295bc08 >> [ 1027.002020] ffffffff8197ef7a ffffea0000b3d300 ffffffff942dd148 dfffe90000000000 >> [ 1027.003359] Call Trace: >> [ 1027.003831] dump_stack (lib/dump_stack.c:52) >> [ 1027.004725] bad_page (mm/page_alloc.c:338) >> [ 1027.005623] free_pages_prepare (mm/page_alloc.c:657 mm/page_alloc.c:763) >> [ 1027.006761] free_hot_cold_page (mm/page_alloc.c:1438) >> [ 1027.007772] ? __page_cache_release (mm/swap.c:66) >> [ 1027.008815] put_page (mm/swap.c:270) >> [ 1027.009665] page_cache_pipe_buf_release (fs/splice.c:93) >> [ 1027.010888] __splice_from_pipe (fs/splice.c:784 fs/splice.c:886) >> [ 1027.011917] ? might_fault (./arch/x86/include/asm/current.h:14 mm/memory.c:3734) >> [ 1027.012856] ? pipe_lock (fs/pipe.c:69) >> [ 1027.013728] ? write_pipe_buf (fs/splice.c:1534) >> [ 1027.014756] vmsplice_to_user (fs/splice.c:1574) >> [ 1027.015725] ? rcu_read_lock_held (kernel/rcu/update.c:169) >> [ 1027.016757] ? __fget_light (include/linux/fdtable.h:80 fs/file.c:684) >> [ 1027.017782] SyS_vmsplice (fs/splice.c:1656 fs/splice.c:1639) >> [ 1027.018863] tracesys_phase2 (arch/x86/kernel/entry_64.S:529) >> > > So what happened here? Userspace fed some mlocked memory into splice() > and then, while splice() was running, userspace dropped its reference > to the memory, leaving splice() with the last reference. Yet somehow, > that page was still marked as being mlocked. I wouldn't expect the > kernel to permit userspace to drop its reference to the memory without > first clearing the mlocked state. I did check a bit and something caught my eye. Both page_remove_rmap() and page_remove_file_rmap() contain this: if (unlikely(PageMlocked(page))) clear_page_mlock(page); So could maybe something mlock the page between the check and clear? I find lru_cache_add_active_or_unevictable somewhat suspicious. But checking if these two could race will take some time. > Is it possible to work out from trinity sources what the exact sequence > was? Which syscalls are being used, for example? > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/