From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933961AbbDJOLr (ORCPT ); Fri, 10 Apr 2015 10:11:47 -0400 Received: from mail-wi0-f179.google.com ([209.85.212.179]:33166 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933785AbbDJOLp (ORCPT ); Fri, 10 Apr 2015 10:11:45 -0400 Date: Fri, 10 Apr 2015 17:11:40 +0300 From: Alexey Dobriyan To: Jarod Wilson Cc: Andrew Morton , linux-kernel@vger.kernel.org, "Eric W. Biederman" , Al Viro , Miklos Szeredi , Zefan Li , Oleg Nesterov Subject: Re: [PATCH] fs/proc: allow larger /proc//cmdline output Message-ID: <20150410141140.GA27200@p183.telecom.by> References: <1428638342-6782-1-git-send-email-jarod@redhat.com> <20150409211200.78b8631e.akpm@linux-foundation.org> <20150410121838.GA13391@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150410121838.GA13391@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 10, 2015 at 08:18:38AM -0400, Jarod Wilson wrote: > On Thu, Apr 09, 2015 at 09:12:00PM -0700, Andrew Morton wrote: > > On Thu, 9 Apr 2015 23:59:02 -0400 Jarod Wilson wrote: > > > > > There are people who run java. Sometimes, when it misbehaves, they try to > > > figure out what's going on by dumping /proc//cmdline, but the length > > > of that output is currently capped by PAGE_SIZE (so x86_64's 4k, in most > > > cases), and sometimes, java command lines are longer than 4k characters. > > > > > > This change allows the user to request a larger max length, up to 4x > > > PAGE_SIZE, but the default out-of-the-box setting should keep things the > > > same as they ever were. The 4x maximum is somewhat arbitrary, but seemed > > > like it should be more than enough, because really, if you have more than > > > 16k characters on your command line, you're probably doing it wrong... > > > > > > I've tested this lightly with non-java shell commands with really long > > > parameters, and things are perfectly stable after several hundred > > > iterations of exercising things on a system booted with both > > > proc_pid_maxlen=8192 and 16384. I wouldn't call my testing exhaustive, > > > and I may not have considered something that will blow up horribly here, > > > so comments and clues welcomed. > > > > > > Using single_open_size() looked less messy than giving proc_pid_cmdline() > > > its own .start op that would allow multiple buffers. > > > > > > Note: I've only added this extended sizing for /proc//cmdline output, > > > rather than for all /proc//foo elements, thinking that nothing else > > > should ever really be that long, but anything that is can simply switch > > > from using the ONE() macro to the ONE_SIZE() macro. > > > > Why have an upper limit at all? > > Just trying to be conservative and keep people from doing anything too > insane, but I didn't really have any particularly good reason beyond that > for capping it. I'll remove the upper bound next iteration. There is no need for next iteration. Andrew has been ignoring real fix for more than a month now! Alexey