From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752700AbeDJIsQ (ORCPT ); Tue, 10 Apr 2018 04:48:16 -0400 Received: from mail-lf0-f45.google.com ([209.85.215.45]:41340 "EHLO mail-lf0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752430AbeDJIsO (ORCPT ); Tue, 10 Apr 2018 04:48:14 -0400 X-Google-Smtp-Source: AIpwx4+QzQjmlyME8jy3KL4CJ7a2VtMxOa0q5hmVtMPM9xctRRJjM/c7df9dnllwcqhfyO/UzrNXkg== Date: Tue, 10 Apr 2018 11:48:10 +0300 From: Cyrill Gorcunov To: Yang Shi Cc: adobriyan@gmail.com, mhocko@kernel.org, willy@infradead.org, mguzik@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [v3 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct Message-ID: <20180410084810.GA2041@uranus.lan> References: <1523310774-40300-1-git-send-email-yang.shi@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1523310774-40300-1-git-send-email-yang.shi@linux.alibaba.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 10, 2018 at 05:52:54AM +0800, Yang Shi wrote: > mmap_sem is on the hot path of kernel, and it very contended, but it is > abused too. It is used to protect arg_start|end and evn_start|end when > reading /proc/$PID/cmdline and /proc/$PID/environ, but it doesn't make > sense since those proc files just expect to read 4 values atomically and > not related to VM, they could be set to arbitrary values by C/R. > > 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 > > Both Alexey Dobriyan and Michal Hocko suggested to use dedicated lock > for them to mitigate the abuse of mmap_sem. > > So, introduce a new spinlock in mm_struct to protect the concurrent > access to arg_start|end, env_start|end and others except start_brk and > brk, which are still protected by mmap_sem to avoid concurrent access > from do_brk(). > > This patch just eliminates the abuse of mmap_sem, but it can't resolve the > above hung task warning completely since the later access_remote_vm() call > needs acquire mmap_sem. The mmap_sem scalability issue will be solved in the > future. > > Signed-off-by: Yang Shi > Cc: Alexey Dobriyan > Cc: Michal Hocko > Cc: Matthew Wilcox > Cc: Mateusz Guzik > Cc: Cyrill Gorcunov > --- > v2 --> v3: > * Restored down_write in prctl syscall > * Elaborate the limitation of this patch suggested by Michal > * Protect those fields by the new lock except brk and start_brk per Michal's > suggestion > * Based off Cyrill's non PR_SET_MM_MAP oprations deprecation patch > (https://lkml.org/lkml/2018/4/5/541) For prctl part Acked-by: Cyrill Gorcunov thanks!