From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sagi Grimberg Subject: Re: [PATCH v1 04/14] xprtrdma: Use ib_device pointer safely Date: Thu, 07 May 2015 16:56:58 +0300 Message-ID: <554B6F2A.6000608@dev.mellanox.co.il> References: <20150504174626.3483.97639.stgit@manet.1015granger.net> <20150504175720.3483.80356.stgit@manet.1015granger.net> <554B37CF.2070206@dev.mellanox.co.il> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Chuck Lever Cc: linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux NFS Mailing List List-Id: linux-rdma@vger.kernel.org On 5/7/2015 4:39 PM, Chuck Lever wrote: > > On May 7, 2015, at 6:00 AM, Sagi Grimberg = wrote: > >> On 5/4/2015 8:57 PM, Chuck Lever wrote: >>> The connect worker can replace ri_id, but prevents ri_id->device >>> from changing during the lifetime of a transport instance. >>> >>> Cache a copy of ri_id->device in rpcrdma_ia and in rpcrdma_rep. >>> The cached copy can be used safely in code that does not serialize >>> with the connect worker. >>> >>> Other code can use it to save an extra address generation (one >>> pointer dereference instead of two). >>> >>> Signed-off-by: Chuck Lever >>> --- >>> net/sunrpc/xprtrdma/fmr_ops.c | 8 +---- >>> net/sunrpc/xprtrdma/frwr_ops.c | 12 +++---- >>> net/sunrpc/xprtrdma/physical_ops.c | 8 +---- >>> net/sunrpc/xprtrdma/verbs.c | 61 +++++++++++++++++++----= ------------- >>> net/sunrpc/xprtrdma/xprt_rdma.h | 2 + >>> 5 files changed, 43 insertions(+), 48 deletions(-) >>> >>> diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fm= r_ops.c >>> index 302d4eb..0a96155 100644 >>> --- a/net/sunrpc/xprtrdma/fmr_ops.c >>> +++ b/net/sunrpc/xprtrdma/fmr_ops.c >>> @@ -85,7 +85,7 @@ fmr_op_map(struct rpcrdma_xprt *r_xprt, struct rp= crdma_mr_seg *seg, >>> int nsegs, bool writing) >>> { >>> struct rpcrdma_ia *ia =3D &r_xprt->rx_ia; >>> - struct ib_device *device =3D ia->ri_id->device; >>> + struct ib_device *device =3D ia->ri_device; >>> enum dma_data_direction direction =3D rpcrdma_data_dir(writing); >>> struct rpcrdma_mr_seg *seg1 =3D seg; >>> struct rpcrdma_mw *mw =3D seg1->rl_mw; >>> @@ -137,17 +137,13 @@ fmr_op_unmap(struct rpcrdma_xprt *r_xprt, str= uct rpcrdma_mr_seg *seg) >>> { >>> struct rpcrdma_ia *ia =3D &r_xprt->rx_ia; >>> struct rpcrdma_mr_seg *seg1 =3D seg; >>> - struct ib_device *device; >>> int rc, nsegs =3D seg->mr_nsegs; >>> LIST_HEAD(l); >>> >>> list_add(&seg1->rl_mw->r.fmr->list, &l); >>> rc =3D ib_unmap_fmr(&l); >>> - read_lock(&ia->ri_qplock); >>> - device =3D ia->ri_id->device; >>> while (seg1->mr_nsegs--) >>> - rpcrdma_unmap_one(device, seg++); >>> - read_unlock(&ia->ri_qplock); >>> + rpcrdma_unmap_one(ia->ri_device, seg++); >> >> Umm, I'm wandering if this is guaranteed to be the same device as >> ri_id->device? >> >> Imagine you are working on a bond device where each slave belongs to >> a different adapter. When the active port toggles, you will see a >> ADDR_CHANGED event (that the current code does not handle...), what >> you'd want to do is just reconnect and rdma_cm will resolve the new >> address for you (via the backup slave). I suspect that in case this >> flow is concurrent with the reconnects you may end up with a stale >> device handle. > > I=92m not sure what you mean by =93stale=94 : freed memory? > > I=92m looking at this code in rpcrdma_ep_connect() : > > 916 if (ia->ri_id->device !=3D id->device) { > 917 printk("RPC: %s: can't reconnect = on " > 918 "different device!\n", __func__= ); > 919 rdma_destroy_id(id); > 920 rc =3D -ENETUNREACH; > 921 goto out; > 922 } > > After reconnecting, if the ri_id has changed, the connect fails. Toda= y, > xprtrdma does not support the device changing out from under it. > > Note also that our receive completion upcall uses ri_id->device for > DMA map syncing. Would that also be a problem during a bond failover? > I'm not talking about ri_id->device, this will be consistent. I'm wandering about ia->ri_device, which might not have been updated yet. Just asking, assuming your transport device can change between=20 consecutive reconnects (the new cm_id will contain another device), is it safe to rely on ri_device being updated? -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" i= n the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html