On Wed, Feb 12, 2014 at 02:57:14PM +0000, Marciniszyn, Mike wrote:
> BTW, I am considering eliminating the atomic_inc() in favor of widening the
> scope of the rcu lock expanse.
As long as the newly included code doesn't block, that should work fine.
(If it does block, another option is SRCU.)
Thanx, Paul
> Mike
>
> > -----Original Message-----
> > From: Paul E. McKenney [mailto:[email protected]]
> > Sent: Wednesday, February 12, 2014 9:56 AM
> > To: Marciniszyn, Mike
> > Cc: [email protected]; Hefty, Sean; [email protected]; linux-
> > [email protected]; [email protected]
> > Subject: Re: qib_lookup_qpn() appears to leak pointer out of
> > rcu_read_unlock()
> >
> > On Wed, Feb 12, 2014 at 01:59:30PM +0000, Marciniszyn, Mike wrote:
> > > > So what am I missing here?
> > > >
> > >
> > > The atomic increment of a reference count:
> >
> > Got it, thank you, apologies for the noise!
> >
> > Thanx, Paul
> >
> > > struct qib_qp *qib_lookup_qpn(struct qib_ibport *ibp, u32 qpn) {
> > > struct qib_qp *qp = NULL;
> > >
> > > rcu_read_lock();
> > > if (unlikely(qpn <= 1)) {
> > > if (qpn == 0)
> > > qp = rcu_dereference(ibp->qp0);
> > > else
> > > qp = rcu_dereference(ibp->qp1);
> > > if (qp)
> > > atomic_inc(&qp->refcount);
> > > <--------------------------
> > > } else {
> > > struct qib_ibdev *dev = &ppd_from_ibp(ibp)->dd->verbs_dev;
> > > unsigned n = qpn_hash(dev, qpn);
> > >
> > > for (qp = rcu_dereference(dev->qp_table[n]); qp;
> > > qp = rcu_dereference(qp->next))
> > > if (qp->ibqp.qp_num == qpn) {
> > > atomic_inc(&qp->refcount);
> > > <---------------------
> > > break;
> > > }
> > > }
> > > rcu_read_unlock();
> > > return qp;
> > > }
> > >
> > > Mike
> > >
>
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