From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751362AbeBTXic (ORCPT ); Tue, 20 Feb 2018 18:38:32 -0500 Received: from out30-132.freemail.mail.aliyun.com ([115.124.30.132]:51660 "EHLO out30-132.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750773AbeBTXib (ORCPT ); Tue, 20 Feb 2018 18:38:31 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R761e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e01422;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0SyIwHO-_1519169905; Subject: Re: [PATCH] fs: proc: use down_read_killable in proc_pid_cmdline_read() To: Alexey Dobriyan Cc: akpm@linux-foundation.org, mingo@kernel.org, linux-kernel@vger.kernel.org References: <1519156169-11883-1-git-send-email-yang.shi@linux.alibaba.com> <20180220223825.GA6705@avx2> From: Yang Shi Message-ID: Date: Tue, 20 Feb 2018 15:38:24 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20180220223825.GA6705@avx2> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/20/18 2:38 PM, Alexey Dobriyan wrote: > On Wed, Feb 21, 2018 at 03:49:29AM +0800, Yang Shi wrote: >> When running vm-scalability with large memory (> 300GB), the below hung >> task issue happens occasionally. >> >> 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 >> >> When manipulating a large mapping, the process may hold the mmap_sem for >> long time, so reading /proc//cmdline may be blocked in >> uninterruptible state for long time. >> >> down_read_trylock() sounds too aggressive, and we already have killable >> version APIs for semaphore, here use down_read_killable() to improve the >> responsiveness. >> - down_read(&mm->mmap_sem); >> + rv = down_read_killable(&mm->mmap_sem); >> + if (rv) >> + goto out_mmput; >> arg_start = mm->arg_start; >> arg_end = mm->arg_end; >> env_start = mm->env_start; > Fix is incomplete Yes, it is. Since I just ran into the above splat, so I just did the minimum change. > 1) /proc/*/cmdline only wants to read 4 values atomically, > those 4 values are basically random values and aren't > related to VM part at all (after C/R went in, they are > settable to arbitrary values) Sorry, I don't get your point here. Could you please elaborate? > 2) access_remote_vm() et al will do the same ->mmap_sem, and Yes, it does. But, __access_remote_vm() is called by access_process_vm() too, which is used by much more places, i.e. ptrace, so I was not sure if it is preferred to convert to killable version. So, I leave it untouched. > 3) /proc/*/environ and get_cmdline() do the same. They look suitable to use killable version. BTW, I just realized the code should go to out_free_page instead of out_mmput. Will rectify in newer version once we decide the extra places to use killable version. Thanks, Yang