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

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Date:   Fri, 10 Jan 2020 10:54:07 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     madhuparnabhowmik04@...il.com
Cc:     jgg@...pe.ca, dennis.dalessandro@...el.com,
        mike.marciniszyn@...el.com, dledford@...hat.com,
        paulmck@...nel.org, rcu@...r.kernel.org, frextrite@...il.com,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] infiniband: hw: hfi1: verbs.c: Use built-in RCU list
 checking

On Wed, Jan 08, 2020 at 01:35:07PM +0530, madhuparnabhowmik04@...il.com wrote:
> From: Jason Gunthorpe <jgg@...pe.ca>
> 
> On Wed, Jan 08, 2020 at 12:59:12AM +0530, madhuparnabhowmik04@...il.com wrote:
> > From: Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
> > 
> > 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@...il.com>
> >  drivers/infiniband/hw/hfi1/verbs.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/infiniband/hw/hfi1/verbs.c b/drivers/infiniband/hw/hfi1/verbs.c
> > index 089e201d7550..e6abdbcb4ffb 100644
> > +++ b/drivers/infiniband/hw/hfi1/verbs.c
> > @@ -515,7 +515,8 @@ static inline void hfi1_handle_packet(struct hfi1_packet *packet,
> >  				       opa_get_lid(packet->dlid, 9B));
> >  		if (!mcast)
> >  			goto drop;
> > -		list_for_each_entry_rcu(p, &mcast->qp_list, list) {
> > +		list_for_each_entry_rcu(p, &mcast->qp_list, list,
> > +					lock_is_held(&(ibp->rvp.lock).dep_map)) {
> 
> Why .dep_map? Does this compile?

Yeah, have you really compiled this? Don't send patches without at least
compile testing !!

> Alternatively, it can be lockdep_is_held(ibp->rvp.lock).
> Please refer to the macro(link below) and let me know if the usage of lock_is_held()
> in the patch is correct.
> 
> https://elixir.bootlin.com/linux/v5.5-rc2/source/include/linux/lockdep.h#L364

Please use lockdep_is_held(). Thanks.

thanks,

 - Joel

> 
> Thanks,
> Madhuparna
> Jason