From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262972AbUBZUKl (ORCPT ); Thu, 26 Feb 2004 15:10:41 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262974AbUBZUKl (ORCPT ); Thu, 26 Feb 2004 15:10:41 -0500 Received: from fw.osdl.org ([65.172.181.6]:8888 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S262972AbUBZUK3 (ORCPT ); Thu, 26 Feb 2004 15:10:29 -0500 Date: Thu, 26 Feb 2004 12:09:59 -0800 From: Andrew Morton To: davidm@hpl.hp.com Cc: davidm@napali.hpl.hp.com, peter@chubb.wattle.id.au, kingsley@aurema.com, linux-kernel@vger.kernel.org, Daniel Jacobowitz Subject: Re: /proc visibility patch breaks GDB, etc. Message-Id: <20040226120959.35b284ff.akpm@osdl.org> In-Reply-To: <16446.19305.637880.99704@napali.hpl.hp.com> References: <16445.37304.155370.819929@wombat.chubb.wattle.id.au> <20040225224410.3eb21312.akpm@osdl.org> <16446.19305.637880.99704@napali.hpl.hp.com> X-Mailer: Sylpheed version 0.9.4 (GTK+ 1.2.10; i686-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 X-Mailing-List: linux-kernel@vger.kernel.org David Mosberger wrote: > > >>>>> On Wed, 25 Feb 2004 22:44:10 -0800, Andrew Morton said: > > Andrew> Peter Chubb wrote: > >> > >> > >> In fs/proc/base.c:proc_pid_lookup(), the patch > >> > >> read_unlock(&tasklist_lock); if (!task) goto out; + if > >> (!thread_group_leader(task)) + goto out_drop_task; > >> > >> inode = proc_pid_make_inode(dir->i_sb, task, PROC_TGID_INO); > >> > >> means that threads other than the thread group leader don't > >> appear in the /proc top-level directory. Programs that are > >> informed via pid of events can no longer find the appropriate > >> process -- for example, using gdb on a multi-threaded process, or > >> profiling using perfmon. > >> > >> The immediate symptom is GDB saying: Could not open > >> /proc/757/status when 757 is a TID not a PID. > > Andrew> What does `ls /proc/757' say? Presumably no such file or > Andrew> directory? It's fairly bizare behaviour to be able to open > Andrew> files which don't exist according to readdir, which is why > Andrew> we made that change. > > Excuse, but this seems seriously FOOBAR. I understand that it's > interesting to see the thread-leader/thread relationship, but surely > that's no reason to break backwards compatibility and the ability to > look up _any_ task's info via /proc/PID/. Well you can't look them up - you can only open them. But I take your point. In another life, these things would appear under a special /proc/magical_directory_which_has_dopey_semantics. > A program that only wants > to show "processes" (thread-group leaders) can simply read > /proc/PID/status and ignore the entries for which Tgid != PPid. > > Perhaps you could put relative symlinks in task/? Something like > this: > > $ ls -l /proc/self/task > dr-xr-xr-x 3 davidm users 0 Feb 26 11:37 13494 -> .. > dr-xr-xr-x 3 davidm users 0 Feb 26 11:37 13495 -> ../../13495 > > perhaps? Well the contents of /proc/pid/task are OK at present. I guess we should revert that change.