Re: [PATCH] use pid_alive in proc_pid_status

[Manfred Spraul]

Ingo Molnar wrote:

> * Andrew Morton <akpm@xxxxxxxx> wrote:
>
>  
>
> > > +int pid_alive(struct task_struct *p)
> > > +{
> > > +	return p->pids[PIDTYPE_PID].nr != 0;
> > > +}
> > >      
> > Can we not simply test p->exit_state?  That's already done in quite a
> > few places and making things consistent would be nice.
> >    
>
> as long as it's accessed from under the tasklist_lock, it ought to be
> fine to check for p->exit_state != EXIT_DEAD and dereference
> p->group_leader afterwards.
>
>  
The tricky part is proc_pid_unhash()/proc_pid_flush(): Right now 
removing a pid from the pid bitmap and disabling /proc/<pid>/* is 
atomic: Both operations are done under tasklist_lock.
I think it would be better to modify pid_alive to p->exit_state and 
disable /proc/<pid>/* access when the exit state is set to DEAD, but 
that that would be a larger change. Probably unhash and flush could be 
merged into one function.
But I don't understand the lines in wait_task_zombie that reset 
exit_state from DEAD to ZOMBIE, so perhaps I overlook something.

--
   Manfred
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