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

From: Dennis Dalessandro <dennis.dalessandro@intel.com>
To: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>,
	Jason Gunthorpe <jgg@ziepe.ca>
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 12:24:52 -0500	[thread overview]
Message-ID: <c773894a-b011-2419-683a-3b851583fc73@intel.com> (raw)
In-Reply-To: <CAF65HP0RsW5FMRRf5Lia2=MTKex-KwO7-_NsCUef94YKBg+pfA@mail.gmail.com>

On 2/14/2020 10:43 AM, Madhuparna Bhowmik wrote:
> 
> 
> On Wed, Jan 15, 2020 at 12:05 AM <madhuparnabhowmik04@gmail.com 
> <mailto:madhuparnabhowmik04@gmail.com>> wrote:
> 
>     From: Dennis Dalessandro <dennis.dalessandro@intel.com
>     <mailto: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
>     <mailto:madhuparnabhowmik04@gmail.com> wrote:
>      >>> From: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com
>     <mailto: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 <mailto: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
> 

I've got a patch going through internal discussion and testing for 
adding rcu read locking.

The RDMAVT patch, I was OK with going in, I guess I just mentioned that 
in a reply rather than adding an RB tag. Let me go ahead and do that.

-Denny
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