Re: [PATCH] use pid_alive in proc_pid_status

[Manfred Spraul <manfred@colorfullife.com>]

Ingo Molnar wrote:

>* Andrew Morton <akpm@osdl.org> 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