Re: [PATCH v2 2/2] pid: Remove pidhash

[Rik van Riel]

On Mon, 2017-10-02 at 17:21 +0200, Oleg Nesterov wrote:
> Hi Rik,
> 
> On 10/02, Rik van Riel wrote:
> > 
> > Gargi and I are looking at that code, and trying to figure out
> > exactly what needs to be done to make all of this correct.
> 
> see another email I sent to Gargi a minute ago,
> 
> > 2) With pid_ns_prepare_proc out of the way, we can put all the code
> > ÂÂÂfrom below where the call to pid_ns_prepare_proc is now (except
> > ÂÂÂerror handing) into the main loop of pid allocation, so we can
> > ÂÂÂdo all that stuff under the pidmap_lock:
> > 
> > ÂÂÂfor (i = ns->level; i >= 0; i--) {
> > ÂÂÂÂÂÂÂ...
> > ÂÂÂÂÂÂÂidr_alloc_cyclic(...)
> > ÂÂÂÂÂÂÂget_pid_ns(ns);
> > ÂÂÂÂÂÂÂatomic_set(&pid->count, 1);
> > ÂÂÂÂÂÂÂfor (...)
> > ÂÂÂÂÂÂÂÂÂÂÂÂINIT_HLIST_HEAD(...)
> > ÂÂÂÂÂÂÂns->nr_allocated++;
> > ÂÂÂÂÂÂÂ...
> > Â }
> 
> I do not see how this can fix the problem with not-fully-initialized
> pid returned by find_pid_ns().
> 
> As for PIDNS_ADDING/PIDNS_HASH_ADDING, _perhaps_ we can cleanup this
> logic
> a bit and do the check earlier, but imo this needs another/separate
> change.
> 
> I'd suggest to keep the current logic and the order of initialization
> and
> just do
> 
> 	for (i = ns->level; i >= 0; i--) {
> 		...
> 
> 		// do not expose the new pid to find_pid_ns() until it
> 		// is fully initialized
> 		nr = idr_alloc_cyclic(&tmp->idr, /*pid*/ NULL, ...);
> 		...
> 	}
> 
> 	...
> 
> 	spin_lock_irq(&pidmap_lock);
> 	if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
> 		goto out_unlock;
> 	for ( ; upid >= pid->numbers; --upid) {
> -		hlist_add_head_rcu(&upid->pid_chain,
> -				&pid_hash[pid_hashfn(upid->nr, upid-
> >ns)]);
> +		// finally make it visible to find_pid_ns()
> +		idr_replace(upid->ns-idr, pid, upid->nr);
> 		upid->ns->nr_hashed++;
> 	}
> 	spin_unlock_irq(&pidmap_lock);
> 
> Or I missed something?

You are right, that would both fix the problem, and keep the error
paths relatively simple.

Gargi, what do you think?

-- 
All Rights Reversed.

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