Re: [patch 06/18] oom: avoid sending exiting tasks a SIGKILL

[David Rientjes <rientjes@google.com>]

On Wed, 9 Jun 2010, Oleg Nesterov wrote:

> > I hope that my sentence didn't imply that it was, the point is that
> > sending a SIGKILL to a PF_EXITING task isn't necessary to make it exit,
> > it's already along the right path.
> 
> Well, probably this is right...
> 
> David, currently I do not know how the code looks with all patches
> applied, could you please confirm there is no problem here? I am
> looking at Linus's tree,
> 
> 	mem_cgroup_out_of_memory:
> 
> 		 p = select_bad_process();
> 		 oom_kill_process(p);
> 

mem_cgroup_out_of_memory() does this under tasklist_lock:

retry:
	p = select_bad_process(&points, mem, CONSTRAINT_MEMCG, NULL);
	if (!p || PTR_ERR(p) == -1UL)
		goto out;

	if (oom_kill_process(p, gfp_mask, 0, points, mem,
				"Memory cgroup out of memory"))
		goto retry;
out:
	...

> Now, again, select_bad_process() can return the dead group-leader
> of the memory-hog-thread-group.
> 

select_bad_process() already has:

	if ((p->flags & PF_EXITING) && p->mm) {
		if (p != current)
			return ERR_PTR(-1UL);

		chosen = p;
		*ppoints = ULONG_MAX;
	}

so we can disregard the check for p == current in this case since it would 
not be allocating memory without p->mm.

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