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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id b30sm8824082vkk.22.2019.07.22.08.26.00 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 22 Jul 2019 08:26:00 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hpaCN-0004p6-MM; Mon, 22 Jul 2019 12:25:59 -0300 Date: Mon, 22 Jul 2019 12:25:59 -0300 From: Jason Gunthorpe To: Maksym Planeta Cc: Moni Shoua , Doug Ledford , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 04/10] Protect kref_put with the lock Message-ID: <20190722152559.GD7607@ziepe.ca> References: <20190722151426.5266-1-mplaneta@os.inf.tu-dresden.de> <20190722151426.5266-5-mplaneta@os.inf.tu-dresden.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190722151426.5266-5-mplaneta@os.inf.tu-dresden.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On Mon, Jul 22, 2019 at 05:14:20PM +0200, Maksym Planeta wrote: > Need to ensure that kref_put does not run concurrently with the loop > inside rxe_pool_get_key. > > Signed-off-by: Maksym Planeta > drivers/infiniband/sw/rxe/rxe_pool.c | 18 ++++++++++++++++++ > drivers/infiniband/sw/rxe/rxe_pool.h | 4 +--- > 2 files changed, 19 insertions(+), 3 deletions(-) > > diff --git a/drivers/infiniband/sw/rxe/rxe_pool.c b/drivers/infiniband/sw/rxe/rxe_pool.c > index efa9bab01e02..30a887cf9200 100644 > +++ b/drivers/infiniband/sw/rxe/rxe_pool.c > @@ -536,3 +536,21 @@ void *rxe_pool_get_key(struct rxe_pool *pool, void *key) > read_unlock_irqrestore(&pool->pool_lock, flags); > return node ? elem : NULL; > } > + > +static void rxe_dummy_release(struct kref *kref) > +{ > +} > + > +void rxe_drop_ref(struct rxe_pool_entry *pelem) > +{ > + int res; > + struct rxe_pool *pool = pelem->pool; > + unsigned long flags; > + > + write_lock_irqsave(&pool->pool_lock, flags); > + res = kref_put(&pelem->ref_cnt, rxe_dummy_release); > + write_unlock_irqrestore(&pool->pool_lock, flags); This doesn't make sense.. If something is making the kref go to 0 while the node is still in the RB tree then that is a bug. You should never need to add locking around a kref_put. Jason