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

From: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>
To: dennis.dalessandro@intel.com, Jason Gunthorpe <jgg@ziepe.ca>,
	 madhuparna bhowmik <madhuparnabhowmik04@gmail.com>
Cc: mike.marciniszyn@intel.com,
	"Paul E. McKenney" <paulmck@kernel.org>,
	linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org,
	rcu@vger.kernel.org, Joel Fernandes <joel@joelfernandes.org>,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [Linux-kernel-mentees] [PATCH 1/3] infiniband: hw: hfi1: verbs.c: Use built-in RCU list checking
Date: Fri, 14 Feb 2020 21:13:03 +0530	[thread overview]
Message-ID: <CAF65HP0RsW5FMRRf5Lia2=MTKex-KwO7-_NsCUef94YKBg+pfA@mail.gmail.com> (raw)
In-Reply-To: <25133367-6544-d0af-ae30-5178909748b1@intel.com>

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On Wed, Jan 15, 2020 at 12:05 AM <madhuparnabhowmik04@gmail.com> wrote:

> From: Dennis Dalessandro <dennis.dalessandro@intel.com>
>
> 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@gmail.com wrote:
> >>> From: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.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@gmail.com>
> >>>   drivers/infiniband/hw/hfi1/verbs.c | 2 +-
> >>>   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,
> >>>                          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,
> >>> 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().
>
> I'd say hold off on this and we'll fix it right. Same goes for the qib one.
>
> Alright, thank you for reviewing.
>
> The rdmavt one though looks to be OK. I'll give it a test.
>
> Hi,
I just wanted to follow up on this.
Any updates?
Also, is the bug fixed now?

Thank you,
Madhuparna

> Thank you,
> Madhuparna
>
> -Denny
>

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