From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id 7A2536B0009 for ; Mon, 26 Mar 2018 10:49:28 -0400 (EDT) Received: by mail-pl0-f70.google.com with SMTP id w19-v6so13209123plq.2 for ; Mon, 26 Mar 2018 07:49:28 -0700 (PDT) Received: from www262.sakura.ne.jp (www262.sakura.ne.jp. [202.181.97.72]) by mx.google.com with ESMTPS id p11si11312820pfh.247.2018.03.26.07.49.26 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Mar 2018 07:49:27 -0700 (PDT) Subject: Re: [PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct References: <1521851771-108673-1-git-send-email-yang.shi@linux.alibaba.com> <20180324043044.GA22733@bombadil.infradead.org> From: Tetsuo Handa Message-ID: Date: Mon, 26 Mar 2018 23:49:18 +0900 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Yang Shi , Matthew Wilcox Cc: adobriyan@gmail.com, mhocko@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 2018/03/24 9:36, Yang Shi wrote: > And, the mmap_sem contention may cause unexpected issue like below: > > INFO: task ps:14018 blocked for more than 120 seconds. > Tainted: G E 4.9.79-009.ali3000.alios7.x86_64 #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this > message. > ps D 0 14018 1 0x00000004 > ffff885582f84000 ffff885e8682f000 ffff880972943000 ffff885ebf499bc0 > ffff8828ee120000 ffffc900349bfca8 ffffffff817154d0 0000000000000040 > 00ffffff812f872a ffff885ebf499bc0 024000d000948300 ffff880972943000 > Call Trace: > [] ? __schedule+0x250/0x730 > [] schedule+0x36/0x80 > [] rwsem_down_read_failed+0xf0/0x150 > [] call_rwsem_down_read_failed+0x18/0x30 > [] down_read+0x20/0x40 > [] proc_pid_cmdline_read+0xd9/0x4e0 > [] ? do_filp_open+0xa5/0x100 > [] __vfs_read+0x37/0x150 > [] ? security_file_permission+0x9b/0xc0 > [] vfs_read+0x96/0x130 > [] SyS_read+0x55/0xc0 > [] entry_SYSCALL_64_fastpath+0x1a/0xc5 Yes, but > > Both Alexey Dobriyan and Michal Hocko suggested to use dedicated lock > for them to mitigate the abuse of mmap_sem. > > So, introduce a new rwlock in mm_struct to protect the concurrent access > to arg_start|end and env_start|end. does arg_lock really help? I wonder whether per "struct mm_struct" granularity is needed if arg_lock protects only a few atomic reads. A global lock would be sufficient. Also, even if we succeeded to avoid mmap_sem contention at that location, won't we after all get mmap_sem contention messages a bit later, for access_remote_vm() holds mmap_sem which would lead to traces like above if mmap_sem is already contended? > > Signed-off-by: Yang Shi > Cc: Alexey Dobriyan > Cc: Michal Hocko > --- > fs/proc/base.c | 8 ++++---- > include/linux/mm_types.h | 2 ++ > kernel/fork.c | 1 + > kernel/sys.c | 6 ++++++ > mm/init-mm.c | 1 + > 5 files changed, 14 insertions(+), 4 deletions(-)