From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752234AbbCXVm3 (ORCPT ); Tue, 24 Mar 2015 17:42:29 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:37203 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751876AbbCXVm1 (ORCPT ); Tue, 24 Mar 2015 17:42:27 -0400 Date: Tue, 24 Mar 2015 14:42:25 -0700 From: Andrew Morton To: Alexey Dobriyan Cc: linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk Subject: Re: [PATCH] proc: fix PAGE_SIZE limit of /proc/$PID/cmdline Message-Id: <20150324144225.d1483f70d508c02876efd5b4@linux-foundation.org> In-Reply-To: <20150320175147.GA2127@p183.telecom.by> References: <20150320175147.GA2127@p183.telecom.by> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 20 Mar 2015 20:51:47 +0300 Alexey Dobriyan wrote: > /proc/$PID/cmdline truncates output at PAGE_SIZE. It is easy to see with > > $ cat /proc/self/cmdline $(seq 1037) 2>/dev/null > > However, command line size was never limited to PAGE_SIZE but to 128 KB and > relatively recently limitation was removed altogether. > > seq file interface is not OK, because it kmalloc's for whole output and > open + read(, 1) + sleep will pin arbitrary amounts of kernel memory. > To not do that, limit must be imposed which is incompatible with > arbitrary sized command lines. > > I apologize for hairy code, but this it direct consequence of command line > layout in memory and hacks to support things like "init [3]". > > The loops are "unrolled" otherwise it is either macros which hide > control flow or functions with 7-8 arguments with equal line count. > > There should be real setproctitle(2) or something. > > ... > > fs/proc/base.c | 203 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 194 insertions(+), 9 deletions(-) > I'm desperately trying to think of a reason to not merge this patch :( I haven't seen anyone complain about the PAGE_SIZE limit - can't we pretend we didn't notice? Or tell 'em to switch to powerpc so they get 64k!