From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751843AbeBWS2v (ORCPT ); Fri, 23 Feb 2018 13:28:51 -0500 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:54707 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751447AbeBWS2u (ORCPT ); Fri, 23 Feb 2018 13:28:50 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R371e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07486;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=4;SR=0;TI=SMTPD_---0SyP6j1w_1519410521; 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> <20180221195720.GA639@avx2> From: Yang Shi Message-ID: Date: Fri, 23 Feb 2018 10:28:37 -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: <20180221195720.GA639@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 2/21/18 11:57 AM, Alexey Dobriyan wrote: > On Tue, Feb 20, 2018 at 03:38:24PM -0800, Yang Shi wrote: >> >> 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? > I hoped there is some random spinlock those 4 values could be moved to > but no. > >>> 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. > Yeah, but ->mmap_sem is taken 3 times per /proc/*/cmdline read > and your scalability tests should trigger next backtrace right away. > >>> 3) /proc/*/environ and get_cmdline() do the same. >> They look suitable to use killable version. Had a look at get_cmdline() further. It looks it is not necessary to convert to killable since it is called mainly by audit_exit(), which is called when process or syscall exit, so it might be preferred to wait until the mmap_sem is released. So, it sounds pointless to use down_read_killable(). Thanks, Yang >> >> 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.