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

Oleg Nesterov
2017-09-27T15:45:48Z

On 09/27, Gargi Sharma wrote:
>
> -#define find_next_offset(map, off) \
> - find_next_zero_bit((map)->page, BITS_PER_PAGE, off)
> -

this should go into the previous patch, but this is minor...

> @@ -208,12 +200,10 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>
> upid = pid->numbers + ns->level;
> spin_lock_irq(&pidmap_lock);
> - if (!(ns->nr_hashed & PIDNS_HASH_ADDING))
> + if (!(ns->pid_allocated & PIDNS_ADDING))
> goto out_unlock;
> for ( ; upid >= pid->numbers; --upid) {
> - hlist_add_head_rcu(&upid->pid_chain,
> - &pid_hash[pid_hashfn(upid->nr, upid->ns)]);
> - upid->ns->nr_hashed++;
> + upid->ns->pid_allocated++;

No, this is wrong.

It is too late to check PIDNS_HASH_ADDING/PIDNS_ADDING and increment pid_allocated,
once we call idr_alloc_cyclic() this pid is already "hashed" in that it can be found
by find_pid_ns() with this patch applied.

And of course, it is too late to do atomic_set(&pid->count, 1) and initialize
pid->tasks[type] lists by the same reason.

Oleg.