From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ob0-f174.google.com (mail-ob0-f174.google.com [209.85.214.174]) by kanga.kvack.org (Postfix) with ESMTP id 98FC56B0038 for ; Tue, 9 Dec 2014 21:20:37 -0500 (EST) Received: by mail-ob0-f174.google.com with SMTP id nt9so1650753obb.19 for ; Tue, 09 Dec 2014 18:20:37 -0800 (PST) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id mu8si2003319obc.39.2014.12.09.18.20.35 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 09 Dec 2014 18:20:36 -0800 (PST) Message-ID: <5487ACC5.1010002@oracle.com> Date: Tue, 09 Dec 2014 21:15:33 -0500 From: Sasha Levin MIME-Version: 1.0 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: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Hugh Dickins , "linux-mm@kvack.org" , LKML , Dave Jones , Jens Axboe , Davidlohr Bueso , "Kirill A. Shutemov" , Peter Zijlstra , Rik van Riel , Mel Gorman On 11/18/2014 04:58 PM, Andrew Morton wrote: >> [ 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. > > Is it possible to work out from trinity sources what the exact sequence > was? Which syscalls are being used, for example? Phew, this took a long while but I've bisected it (with good confidence) down to: commit a38246260912ba4a0f8b563704a965a7a97cf3c3 Author: Davidlohr Bueso Date: Wed Dec 3 18:54:27 2014 +1100 mm/memory.c: share the i_mmap_rwsem The unmap_mapping_range family of functions do the unmapping of user pages (ultimately via zap_page_range_single) without touching the actual interval tree, thus share the lock. Signed-off-by: Davidlohr Bueso Cc: "Kirill A. Shutemov" Acked-by: Hugh Dickins Cc: Oleg Nesterov Cc: Peter Zijlstra (Intel) Cc: Rik van Riel Cc: Srikar Dronamraju Acked-by: Mel Gorman Signed-off-by: Andrew Morton Thanks, Sasha -- 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