From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 5/5] IB/hfi1: Fix improper uses of smp_mb__before_atomic() Date: Tue, 30 Apr 2019 10:28:14 +0200 Message-ID: <20190430082814.GC2677@hirez.programming.kicks-ass.net> References: <1556568902-12464-1-git-send-email-andrea.parri@amarulasolutions.com> <1556568902-12464-6-git-send-email-andrea.parri@amarulasolutions.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1556568902-12464-6-git-send-email-andrea.parri@amarulasolutions.com> Sender: linux-kernel-owner@vger.kernel.org To: Andrea Parri Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Dennis Dalessandro , Mike Marciniszyn , Doug Ledford , Jason Gunthorpe , linux-rdma@vger.kernel.org List-Id: linux-rdma@vger.kernel.org On Mon, Apr 29, 2019 at 10:15:01PM +0200, Andrea Parri wrote: > This barrier only applies to the read-modify-write operations; in > particular, it does not apply to the atomic_read() primitive. > > Replace the barrier with an smp_mb(). > > Fixes: 856cc4c237add ("IB/hfi1: Add the capability for reserved operations") > Cc: stable@vger.kernel.org > Reported-by: "Paul E. McKenney" > Reported-by: Peter Zijlstra > Signed-off-by: Andrea Parri > Cc: Dennis Dalessandro > Cc: Mike Marciniszyn > Cc: Doug Ledford > Cc: Jason Gunthorpe > Cc: linux-rdma@vger.kernel.org > --- > drivers/infiniband/sw/rdmavt/qp.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/infiniband/sw/rdmavt/qp.c b/drivers/infiniband/sw/rdmavt/qp.c > index a34b9a2a32b60..b64fd151d31fb 100644 > --- a/drivers/infiniband/sw/rdmavt/qp.c > +++ b/drivers/infiniband/sw/rdmavt/qp.c > @@ -1863,11 +1863,11 @@ static inline int rvt_qp_is_avail( > u32 reserved_used; > > /* see rvt_qp_wqe_unreserve() */ I see a completely bogus comment in rvf_op_wqe_unreserve(), referring to bogus comments makes this barrier bogus too. > - smp_mb__before_atomic(); > + smp_mb(); > reserved_used = atomic_read(&qp->s_reserved_used); > if (unlikely(reserved_op)) { > /* see rvt_qp_wqe_unreserve() */ > - smp_mb__before_atomic(); This was before, but there is nothing _after_ this. Which means this barrier was complete garbage anyway. > + smp_mb(); > if (reserved_used >= rdi->dparms.reserved_operations) > return -ENOMEM; > return 0; > @@ -1882,7 +1882,7 @@ static inline int rvt_qp_is_avail( > avail = slast - qp->s_head; > > /* see rvt_qp_wqe_unreserve() */ > - smp_mb__before_atomic(); > + smp_mb(); Same as the first. > reserved_used = atomic_read(&qp->s_reserved_used); > avail = avail - 1 - > (rdi->dparms.reserved_operations - reserved_used);