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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id t2sm10048103qth.33.2019.07.08.12.38.14 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 08 Jul 2019 12:38:15 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hkZSo-0006yC-Dz; Mon, 08 Jul 2019 16:38:14 -0300 Date: Mon, 8 Jul 2019 16:38:14 -0300 From: Jason Gunthorpe To: Mark Bloch Cc: Dag Moxnes , "dledford@redhat.com" , "leon@kernel.org" , Parav Pandit , "linux-rdma@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3] RDMA/core: Fix race when resolving IP address Message-ID: <20190708193814.GF23996@ziepe.ca> References: <1562584584-13132-1-git-send-email-dag.moxnes@oracle.com> <20190708175025.GA6976@ziepe.ca> <4b9ae7b8-310c-e0b6-7a8e-33e6d5bef83d@oracle.com> <63b9d2cb-f69c-d77c-7803-f08e2a6f755d@mellanox.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <63b9d2cb-f69c-d77c-7803-f08e2a6f755d@mellanox.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 08, 2019 at 07:22:45PM +0000, Mark Bloch wrote: > > > On 7/8/19 11:47 AM, Dag Moxnes wrote: > > Thanks Jason, > > > > Regards, > > Dag > > > > Den 08.07.2019 19:50, skrev Jason Gunthorpe: > >> On Mon, Jul 08, 2019 at 01:16:24PM +0200, Dag Moxnes wrote: > >>> Use neighbour lock when copying MAC address from neighbour data struct > >>> in dst_fetch_ha. > >>> > >>> When not using the lock, it is possible for the function to race with > >>> neigh_update, causing it to copy an invalid MAC address. > >>> > >>> It is possible to provoke this error by calling rdma_resolve_addr in a > >>> tight loop, while deleting the corresponding ARP entry in another tight > >>> loop. > >>> > >>> This will cause the race shown it the following sample trace: > >>> > >>> rdma_resolve_addr() > >>>    rdma_resolve_ip() > >>>      addr_resolve() > >>>        addr_resolve_neigh() > >>>          fetch_ha() > >>>            dst_fetch_ha() > >>>              n->nud_state == NUD_VALID > >> It isn't nud_state that is the problem here, it is the parallel > >> memcpy's onto ha. I fixed the commit message > >> > >> This could also have been solved by using the ha_lock, but I don't > >> think we have a reason to particularly over-optimize this. > > Sorry I'm late to the party, but why not just use: neigh_ha_snapshot()? Yes, that is much better, please respin this Thanks, Jason