On Mon, Jul 1, 2013 at 9:49 AM, Rob Landley <[email protected]> wrote: > On 06/26/2013 04:05:01 PM, Andy Lutomirski wrote: >> >> I was surprised to discover that a process can have a parent that isn't >> a thread group leader. (The usual ppid interfaces hide this, but the >> children list exposes it.) >> >> Signed-off-by: Andy Lutomirski <[email protected]> >> Cc: Cyrill Gorcunov <[email protected]> >> Cc: Oleg Nesterov <[email protected]> >> --- >> Documentation/filesystems/proc.txt | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/Documentation/filesystems/proc.txt >> b/Documentation/filesystems/proc.txt >> index fd8d0d5..205796a 100644 >> --- a/Documentation/filesystems/proc.txt >> +++ b/Documentation/filesystems/proc.txt >> @@ -1623,6 +1623,12 @@ This file provides a fast way to retrieve first >> level children pids >> of a task pointed by <pid>/<tid> pair. The format is a space separated >> stream of pids. >> >> +This really is a per-thread list. If a process's parent is a thread, >> +then that process will appear in that thread's children list. (This >> +means that, for any pid, /proc/pid/task/*/children are disjoint lists.) >> +This may be surprising, as /proc/pid/status's PPid field is parent's >> +tgid as opposed to the parent's tid. > > > I've read this twice and still don't quite understand what it's saying. > (Possibly I need more than 3 hours of sleep.) > > It sounds like you're saying a thread can fork() and exec() and this makes > proc look weird, because the ppid pooints to the thread group leader and not > the thread, but the proc info listing us as a child belongs to the thread?
That is exactly right. Is it unclear because I wrote it badly, or is it unclear because it's really weird? Perhaps I'll add something like: For example, if thread group 100 has threads 100 (the leader) and 101, and thread 101 forks and produces a child with tgid 102, then /proc/100/task/100/children will be empty, /proc/100/task/101/children will contain 102, and /proc/102/status will show 'Ppid: 100'. > > Is this a bug that should be fixed rather than documented? (Showing the > right ppid for this corner case?) > I'm not qualified to say whether it's a bug or even, if it is a bug, what the preferred behavior would be. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
