Re: [PATCH 1/3] infiniband: hw: hfi1: verbs.c: Use built-in RCU list checking

[Dennis Dalessandro]

On 1/14/2020 2:41 PM, Jason Gunthorpe wrote:
> On Tue, Jan 14, 2020 at 01:24:00PM -0500, Dennis Dalessandro wrote:
> > On 1/14/2020 12:00 PM, Dennis Dalessandro wrote:
> > > On 1/14/2020 11:57 AM, Jason Gunthorpe wrote:
> > > > On Tue, Jan 14, 2020 at 09:53:45PM +0530,
> > > > madhuparnabhowmik04@xxxxxxxxx wrote:
> > > > > From: Madhuparna Bhowmik <madhuparnabhowmik04@xxxxxxxxx>
> > > > >
> > > > > list_for_each_entry_rcu has built-in RCU and lock checking.
> > > > > Pass cond argument to list_for_each_entry_rcu.
> > > > >
> > > > > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik04@xxxxxxxxx>
> > > > >  Â drivers/infiniband/hw/hfi1/verbs.c | 2 +-
> > > > >  Â 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/infiniband/hw/hfi1/verbs.c
> > > > > b/drivers/infiniband/hw/hfi1/verbs.c
> > > > > index 089e201d7550..22f2d4fd2577 100644
> > > > > +++ b/drivers/infiniband/hw/hfi1/verbs.c
> > > > > @@ -515,7 +515,7 @@ static inline void hfi1_handle_packet(struct
> > > > > hfi1_packet *packet,
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ opa_get_lid(packet->dlid, 9B));
> > > > >  ÂÂÂÂÂÂÂÂÂ if (!mcast)
> > > > >  ÂÂÂÂÂÂÂÂÂÂÂÂÂ goto drop;
> > > > > -ÂÂÂÂÂÂÂ list_for_each_entry_rcu(p, &mcast->qp_list, list) {
> > > > > +ÂÂÂÂÂÂÂ list_for_each_entry_rcu(p, &mcast->qp_list, list,
> > > > > lockdep_is_held(&(ibp->rvp.lock))) {
> > > >
> > > > Okay, this looks reasonable
> > > >
> > > > Mike, Dennis, is this the right lock to test?
> > >
> > > I'm looking at that right now actually, I don't think this is correct.
> > > Wanted to talk to Mike before I send a response though.
> > >
> > > -Denny
> >
> > That's definitely going to throw a ton of lock dep messages. It's not really
> > the right lock either. Instead what we probably need to do is what we do in
> > the non-multicast part of the code and take the rcu_read_lock().
>
> Uh.. why is this using the _rcu varient without holding the rcu lock?
> That is quite wrong already.

Yep, seems like a bug to me. Patch forthcoming.

-Denny