Re: More waitpid issues with CLONE_DETACHED/CLONE_THREAD

[Linus Torvalds]

On Sat, 31 Jan 2004, Daniel Jacobowitz wrote:
> > 
> > Can you verify that that process doesn't have any sub-threads? (Again, 
> > that should be easily visible in /proc/<pid>/task/).
> 
> It is quite easily visible - in fact, it's hilarious.
> 
>  8454 pts/8    Z      0:00 [linux-dp] <defunct>
> 
> drow@nevyn:~% ls /proc/8454
> auxv  cmdline  cwd@  environ  exe@  fd/  maps  mem  mounts  root@  stat
> 
> drow@nevyn:~% ls /proc/8454/task
> ls: /proc/8454/task: No such file or directory

Oh damn. Yeah, we don't allow you to even see the threads in this case (it
checks "pid_alive(task)". We don't want you to try to confuse things by 
opening files of processes that we think are dead.

For the case of trying to figure out sub-threads of a dead thread group
leader, that may actually be a bug.

Just for testing this, you might remove the check for

        if (!pid_alive(task))
                goto out;

in proc_pident_lookup() in fs/proc/base.c.

Ingo - comments? We really want the sysadmin to be able to find threads 
that have a dead group leader, and right now that seems to be impossible.

		Linus
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