> On Apr 26, 2016, at 4:26 PM, Sagi Grimberg <sagi@xxxxxxxxxxx> wrote:
>
>
>
> On 25/04/16 22:22, Chuck Lever wrote:
>> There needs to be a safe method of releasing registered memory
>> resources when an RPC terminates. Safe can mean a number of things:
>>
>> + Doesn't have to sleep
>>
>> + Doesn't rely on having a QP in RTS
>>
>> ro_unmap_safe will be that safe method. It can be used in cases
>> where synchronous memory invalidation can deadlock, or needs to have
>> an active QP.
>>
>> The important case is fencing an RPC's memory regions after it is
>> signaled (^C) and before it exits. If this is not done, there is a
>> window where the server can write an RPC reply into memory that the
>> client has released and re-used for some other purpose.
>>
>> Note that this is a full solution for FRWR, but FMR and physical
>> still have some gaps where a particularly bad server can wreak
>> some havoc on the client. These gaps are not made worse by this
>> patch and are expected to be exceptionally rare and timing-based.
>> They are noted in documenting comments.
>>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> net/sunrpc/xprtrdma/fmr_ops.c | 105 +++++++++++++++++++++++++++++++++---
>> net/sunrpc/xprtrdma/frwr_ops.c | 27 +++++++++
>> net/sunrpc/xprtrdma/physical_ops.c | 20 +++++++
>> net/sunrpc/xprtrdma/rpc_rdma.c | 5 --
>> net/sunrpc/xprtrdma/transport.c | 9 +--
>> net/sunrpc/xprtrdma/xprt_rdma.h | 3 +
>> 6 files changed, 150 insertions(+), 19 deletions(-)
>>
>> diff --git a/net/sunrpc/xprtrdma/fmr_ops.c b/net/sunrpc/xprtrdma/fmr_ops.c
>> index 9d50f3a..a658dcf 100644
>> --- a/net/sunrpc/xprtrdma/fmr_ops.c
>> +++ b/net/sunrpc/xprtrdma/fmr_ops.c
>> @@ -35,6 +35,64 @@
>> /* Maximum scatter/gather per FMR */
>> #define RPCRDMA_MAX_FMR_SGES (64)
>>
>> +static struct workqueue_struct *fmr_recovery_wq;
>> +
>> +#define FMR_RECOVERY_WQ_FLAGS (WQ_UNBOUND)
>> +
>> +int
>> +fmr_alloc_recovery_wq(void)
>> +{
>> + fmr_recovery_wq = alloc_workqueue("fmr_recovery", WQ_UNBOUND, 0);
>> + return !fmr_recovery_wq ? -ENOMEM : 0;
>> +}
>> +
>> +void
>> +fmr_destroy_recovery_wq(void)
>> +{
>> + struct workqueue_struct *wq;
>> +
>> + if (!fmr_recovery_wq)
>> + return;
>> +
>> + wq = fmr_recovery_wq;
>> + fmr_recovery_wq = NULL;
>> + destroy_workqueue(wq);
>> +}
>> +
>> +static int
>> +__fmr_unmap(struct rpcrdma_mw *mw)
>> +{
>> + LIST_HEAD(l);
>> +
>> + list_add(&mw->fmr.fmr->list, &l);
>> + return ib_unmap_fmr(&l);
>> +}
>> +
>> +/* Deferred reset of a single FMR. Generate a fresh rkey by
>> + * replacing the MR. There's no recovery if this fails.
>> + */
>> +static void
>> +__fmr_recovery_worker(struct work_struct *work)
>> +{
>> + struct rpcrdma_mw *mw = container_of(work, struct rpcrdma_mw,
>> + mw_work);
>> + struct rpcrdma_xprt *r_xprt = mw->mw_xprt;
>> +
>> + __fmr_unmap(mw);
>> + rpcrdma_put_mw(r_xprt, mw);
>> + return;
>> +}
>> +
>> +/* A broken MR was discovered in a context that can't sleep.
>> + * Defer recovery to the recovery worker.
>> + */
>> +static void
>> +__fmr_queue_recovery(struct rpcrdma_mw *mw)
>> +{
>> + INIT_WORK(&mw->mw_work, __fmr_recovery_worker);
>> + queue_work(fmr_recovery_wq, &mw->mw_work);
>> +}
>> +
>> static int
>> fmr_op_open(struct rpcrdma_ia *ia, struct rpcrdma_ep *ep,
>> struct rpcrdma_create_data_internal *cdata)
>> @@ -92,6 +150,7 @@ fmr_op_init(struct rpcrdma_xprt *r_xprt)
>> if (IS_ERR(r->fmr.fmr))
>> goto out_fmr_err;
>>
>> + r->mw_xprt = r_xprt;
>> list_add(&r->mw_list, &buf->rb_mws);
>> list_add(&r->mw_all, &buf->rb_all);
>> }
>> @@ -107,15 +166,6 @@ out:
>> return rc;
>> }
>>
>> -static int
>> -__fmr_unmap(struct rpcrdma_mw *r)
>> -{
>> - LIST_HEAD(l);
>> -
>> - list_add(&r->fmr.fmr->list, &l);
>> - return ib_unmap_fmr(&l);
>> -}
>> -
>> /* Use the ib_map_phys_fmr() verb to register a memory region
>> * for remote access via RDMA READ or RDMA WRITE.
>> */
>> @@ -242,6 +292,42 @@ fmr_op_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
>> req->rl_nchunks = 0;
>> }
>>
>> +/* Use a slow, safe mechanism to invalidate all memory regions
>> + * that were registered for "req".
>> + *
>> + * In the asynchronous case, DMA unmapping occurs first here
>> + * because the rpcrdma_mr_seg is released immediately after this
>> + * call. It's contents won't be available in __fmr_dma_unmap later.
>> + * FIXME.
>> + */
>> +static void
>> +fmr_op_unmap_safe(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
>> + bool sync)
>> +{
>> + struct rpcrdma_mr_seg *seg;
>> + struct rpcrdma_mw *mw;
>> + unsigned int i;
>> +
>> + for (i = 0; req->rl_nchunks; req->rl_nchunks--) {
>> + seg = &req->rl_segments[i];
>> + mw = seg->rl_mw;
>> +
>> + if (sync) {
>> + /* ORDER */
>> + __fmr_unmap(mw);
>> + __fmr_dma_unmap(r_xprt, seg);
>> + rpcrdma_put_mw(r_xprt, mw);
>> + } else {
>> + __fmr_dma_unmap(r_xprt, seg);
>> + __fmr_queue_recovery(mw);
>> + }
>> +
>> + i += seg->mr_nsegs;
>> + seg->mr_nsegs = 0;
>> + seg->rl_mw = NULL;
>> + }
>> +}
>> +
>> /* Use the ib_unmap_fmr() verb to prevent further remote
>> * access via RDMA READ or RDMA WRITE.
>> */
>> @@ -295,6 +381,7 @@ fmr_op_destroy(struct rpcrdma_buffer *buf)
>> const struct rpcrdma_memreg_ops rpcrdma_fmr_memreg_ops = {
>> .ro_map = fmr_op_map,
>> .ro_unmap_sync = fmr_op_unmap_sync,
>> + .ro_unmap_safe = fmr_op_unmap_safe,
>> .ro_unmap = fmr_op_unmap,
>> .ro_open = fmr_op_open,
>> .ro_maxpages = fmr_op_maxpages,
>> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
>> index 1251a1d..79ba323 100644
>> --- a/net/sunrpc/xprtrdma/frwr_ops.c
>> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
>> @@ -614,6 +614,32 @@ reset_mrs:
>> goto unmap;
>> }
>>
>> +/* Use a slow, safe mechanism to invalidate all memory regions
>> + * that were registered for "req".
>> + */
>> +static void
>> +frwr_op_unmap_safe(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
>> + bool sync)
>> +{
>> + struct rpcrdma_mr_seg *seg;
>> + struct rpcrdma_mw *mw;
>> + unsigned int i;
>> +
>> + for (i = 0; req->rl_nchunks; req->rl_nchunks--) {
>> + seg = &req->rl_segments[i];
>> + mw = seg->rl_mw;
>> +
>> + if (sync)
>> + __frwr_reset_and_unmap(r_xprt, mw);
>> + else
>> + __frwr_queue_recovery(mw);
>> +
>> + i += seg->mr_nsegs;
>> + seg->mr_nsegs = 0;
>> + seg->rl_mw = NULL;
>> + }
>> +}
>> +
>> /* Post a LOCAL_INV Work Request to prevent further remote access
>> * via RDMA READ or RDMA WRITE.
>> */
>> @@ -675,6 +701,7 @@ frwr_op_destroy(struct rpcrdma_buffer *buf)
>> const struct rpcrdma_memreg_ops rpcrdma_frwr_memreg_ops = {
>> .ro_map = frwr_op_map,
>> .ro_unmap_sync = frwr_op_unmap_sync,
>> + .ro_unmap_safe = frwr_op_unmap_safe,
>> .ro_unmap = frwr_op_unmap,
>> .ro_open = frwr_op_open,
>> .ro_maxpages = frwr_op_maxpages,
>> diff --git a/net/sunrpc/xprtrdma/physical_ops.c b/net/sunrpc/xprtrdma/physical_ops.c
>> index 2dc6ec2..95ef3a7 100644
>> --- a/net/sunrpc/xprtrdma/physical_ops.c
>> +++ b/net/sunrpc/xprtrdma/physical_ops.c
>> @@ -97,6 +97,25 @@ physical_op_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
>> rpcrdma_unmap_one(device, &req->rl_segments[i++]);
>> }
>>
>> +/* Use a slow, safe mechanism to invalidate all memory regions
>> + * that were registered for "req".
>> + *
>> + * For physical memory registration, there is no good way to
>> + * fence a single MR that has been advertised to the server. The
>> + * client has already handed the server an R_key that cannot be
>> + * invalidated and is shared by all MRs on this connection.
>> + * Tearing down the PD might be the only safe choice, but it's
>> + * not clear that a freshly acquired DMA R_key would be different
>> + * than the one used by the PD that was just destroyed.
>> + * FIXME.
>> + */
>> +static void
>> +physical_op_unmap_safe(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req,
>> + bool sync)
>> +{
>> + physical_op_unmap_sync(r_xprt, req);
>> +}
>> +
>
> So physical has no async mode?
Nope. There's no way to fence memory once a client has
exposed its whole-memory R_key.
The client could drop its connection and delete the PD.
> Is there a device that makes you resort to physical memreg?
I'm not aware of one.
> It's an awful lot of maintenance on what looks to be a esoteric (at
> best) code path.
It's never chosen by falling back to that mode.
physical has long been on the chopping block. Last time
I suggested removing it I got a complaint. But there's no
in-kernel device that requires this mode, so seems like
it should go sooner rather than later.
> The rest looks fine to me.
--
Chuck Lever
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