Re: getting processor numbers

[Oleg Nesterov]

On 04/04, Ingo Molnar wrote:
> 
> * Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
> 
> > But we don't need tasklist_lock at all, we can use 
> > rcu_read_lock/unlock. Q: don't we need task_rq_lock() to read 
> > ->cpus_allowed "atomically" ?
> 
> right now ->cpus_allowed is protected by tasklist_lock. We cannot do RCU 
> here because ->cpus_allowed modifications are not RCUified.

Is it so? that was my question. Afaics, set_cpus_allowed() does
p->cpus_allowed = new_mask under rq->lock, so I don't understand
how tasklist_lock can help.

Could you clarify?

Oleg.

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