Messages in this thread | | | Date | Fri, 27 Feb 2004 08:59:41 +1100 | From | Kingsley Cheung <> | Subject | Re: /proc visibility patch breaks GDB, etc. |
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On Thu, Feb 26, 2004 at 12:09:59PM -0800, Andrew Morton wrote: > David Mosberger <davidm@napali.hpl.hp.com> wrote: > > > > >>>>> On Wed, 25 Feb 2004 22:44:10 -0800, Andrew Morton <akpm@osdl.org> said: > > > > Andrew> Peter Chubb <peter@chubb.wattle.id.au> 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.
Ah, so there was some fundamental reason behind that behaviour! Perhaps then a comment or two in the code to explain that such behaviour (prior to change) is intended in proc_pid_lookup()? That way it will be clear that is intended behaviour.
Am I correct to assume though that the corresponding change in proc_task_lookup() should stay? The existing behaviour there was that one could do say,
cat /proc/<pid>/task/<tid>/stat, where tid could be any thread and not a part of the thread group pid.
The patch that broke backwards compatibility for GDB likewise changed that. It enforces that tid must be a part of the pid thread group.
-- Kingsley - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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