From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754966AbeBWTpz (ORCPT ); Fri, 23 Feb 2018 14:45:55 -0500 Received: from mail-wr0-f193.google.com ([209.85.128.193]:43224 "EHLO mail-wr0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754827AbeBWTpv (ORCPT ); Fri, 23 Feb 2018 14:45:51 -0500 X-Google-Smtp-Source: AH8x227DrlxBp/9vQi1KGVsy28aG2osuflRR9zAMEmS2+Tx6uLhWWbAmjr42qRU+VFCqVUZzuALmVA== Date: Fri, 23 Feb 2018 22:45:47 +0300 From: Alexey Dobriyan To: Yang Shi Cc: akpm@linux-foundation.org, mingo@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] fs: proc: use down_read_killable in proc_pid_cmdline_read() Message-ID: <20180223194547.GC5708@avx2> References: <1519156169-11883-1-git-send-email-yang.shi@linux.alibaba.com> <20180220223825.GA6705@avx2> <20180221195720.GA639@avx2> <20180223193338.GA5708@avx2> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.7.2 (2016-11-26) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 23, 2018 at 11:42:34AM -0800, Yang Shi wrote: > > > On 2/23/18 11:33 AM, Alexey Dobriyan wrote: > > On Wed, Feb 21, 2018 at 03:13:10PM -0800, Yang Shi wrote: > > > >>>>> 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. > >> Yes, however, I didn't run into it if mmap_sem is acquired earlier. > >> > >> How about defining a killable version, like > >> __access_remote_vm_killable() which use down_read_killable(), then the > >> killable version can be used by proc/*/cmdline? There might be other > >> users in the future. > > It would be a disaster as interfaces multiply. > > Might be not that bad. Maybe. But you need to explain why there is no backtrace several lines later: access_remote_vm __access_remote_vm down_read(&mm->mmap_sem)