From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 432EE6B000C for ; Mon, 26 Mar 2018 11:31:27 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id i137so5517263pfe.0 for ; Mon, 26 Mar 2018 08:31:27 -0700 (PDT) Received: from out30-131.freemail.mail.aliyun.com (out30-131.freemail.mail.aliyun.com. [115.124.30.131]) by mx.google.com with ESMTPS id z16-v6si15904448pll.36.2018.03.26.08.31.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Mar 2018 08:31:26 -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: Yang Shi Message-ID: <579be4ee-58d0-1ffd-6b73-0202c7b28f08@linux.alibaba.com> Date: Mon, 26 Mar 2018 11:31:03 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa , Matthew Wilcox Cc: adobriyan@gmail.com, mhocko@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 3/26/18 10:49 AM, Tetsuo Handa wrote: > 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. However, a global lock might be hard to know what it is used for, and might be abused again. And, it may introduce unexpected contention for parallel reading for /proc > > 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? Yes, definitely, this patch is aimed to remove the abuse to mmap_sem. The mmap_sem contention will be addressed separately. Yang > >> 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(-)