Re: [PATCH RFC 05/12] xprtrdma: Remove fr_state

[Anna Schumaker <schumaker.anna@gmail.com>]

Hi Chuck,

On Tue, 2019-05-28 at 14:21 -0400, Chuck Lever wrote:
> Since both the Send and Receive completion queues are processed in
> a workqueue context, it should be safe to DMA unmap and return MRs
> to the free or recycle lists directly in the completion handlers.
> 
> Doing this means rpcrdma_frwr no longer needs to track the state
> of each MR... a VALID or FLUSHED MR can no longer appear on an
> xprt's MR free list.
> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/trace/events/rpcrdma.h  |   19 ----
>  net/sunrpc/xprtrdma/frwr_ops.c  |  202 ++++++++++++++++++------------------
> ---
>  net/sunrpc/xprtrdma/rpc_rdma.c  |    2 
>  net/sunrpc/xprtrdma/xprt_rdma.h |   11 --
>  4 files changed, 95 insertions(+), 139 deletions(-)
> 
> diff --git a/include/trace/events/rpcrdma.h b/include/trace/events/rpcrdma.h
> index a4ab3a2..7fe21ba 100644
> --- a/include/trace/events/rpcrdma.h
> +++ b/include/trace/events/rpcrdma.h
> @@ -181,18 +181,6 @@
>  				),					\
>  				TP_ARGS(task, mr, nsegs))
>  
> -TRACE_DEFINE_ENUM(FRWR_IS_INVALID);
> -TRACE_DEFINE_ENUM(FRWR_IS_VALID);
> -TRACE_DEFINE_ENUM(FRWR_FLUSHED_FR);
> -TRACE_DEFINE_ENUM(FRWR_FLUSHED_LI);
> -
> -#define xprtrdma_show_frwr_state(x)					\
> -		__print_symbolic(x,					\
> -				{ FRWR_IS_INVALID, "INVALID" },		\
> -				{ FRWR_IS_VALID, "VALID" },		\
> -				{ FRWR_FLUSHED_FR, "FLUSHED_FR" },	\
> -				{ FRWR_FLUSHED_LI, "FLUSHED_LI" })
> -
>  DECLARE_EVENT_CLASS(xprtrdma_frwr_done,
>  	TP_PROTO(
>  		const struct ib_wc *wc,
> @@ -203,22 +191,19 @@
>  
>  	TP_STRUCT__entry(
>  		__field(const void *, mr)
> -		__field(unsigned int, state)
>  		__field(unsigned int, status)
>  		__field(unsigned int, vendor_err)
>  	),
>  
>  	TP_fast_assign(
>  		__entry->mr = container_of(frwr, struct rpcrdma_mr, frwr);
> -		__entry->state = frwr->fr_state;
>  		__entry->status = wc->status;
>  		__entry->vendor_err = __entry->status ? wc->vendor_err : 0;
>  	),
>  
>  	TP_printk(
> -		"mr=%p state=%s: %s (%u/0x%x)",
> -		__entry->mr, xprtrdma_show_frwr_state(__entry->state),
> -		rdma_show_wc_status(__entry->status),
> +		"mr=%p: %s (%u/0x%x)",
> +		__entry->mr, rdma_show_wc_status(__entry->status),
>  		__entry->status, __entry->vendor_err
>  	)
>  );
> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
> index ac47314..99871fbf 100644
> --- a/net/sunrpc/xprtrdma/frwr_ops.c
> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
> @@ -168,7 +168,6 @@ int frwr_init_mr(struct rpcrdma_ia *ia, struct rpcrdma_mr
> *mr)
>  		goto out_list_err;
>  
>  	mr->frwr.fr_mr = frmr;
> -	mr->frwr.fr_state = FRWR_IS_INVALID;
>  	mr->mr_dir = DMA_NONE;
>  	INIT_LIST_HEAD(&mr->mr_list);
>  	INIT_WORK(&mr->mr_recycle, frwr_mr_recycle_worker);
> @@ -298,65 +297,6 @@ size_t frwr_maxpages(struct rpcrdma_xprt *r_xprt)
>  }
>  
>  /**
> - * frwr_wc_fastreg - Invoked by RDMA provider for a flushed FastReg WC
> - * @cq:	completion queue (ignored)
> - * @wc:	completed WR
> - *
> - */
> -static void
> -frwr_wc_fastreg(struct ib_cq *cq, struct ib_wc *wc)
> -{
> -	struct ib_cqe *cqe = wc->wr_cqe;
> -	struct rpcrdma_frwr *frwr =
> -			container_of(cqe, struct rpcrdma_frwr, fr_cqe);
> -
> -	/* WARNING: Only wr_cqe and status are reliable at this point */
> -	if (wc->status != IB_WC_SUCCESS)
> -		frwr->fr_state = FRWR_FLUSHED_FR;
> -	trace_xprtrdma_wc_fastreg(wc, frwr);
> -}
> -
> -/**
> - * frwr_wc_localinv - Invoked by RDMA provider for a flushed LocalInv WC
> - * @cq:	completion queue (ignored)
> - * @wc:	completed WR
> - *
> - */
> -static void
> -frwr_wc_localinv(struct ib_cq *cq, struct ib_wc *wc)
> -{
> -	struct ib_cqe *cqe = wc->wr_cqe;
> -	struct rpcrdma_frwr *frwr = container_of(cqe, struct rpcrdma_frwr,
> -						 fr_cqe);
> -
> -	/* WARNING: Only wr_cqe and status are reliable at this point */
> -	if (wc->status != IB_WC_SUCCESS)
> -		frwr->fr_state = FRWR_FLUSHED_LI;
> -	trace_xprtrdma_wc_li(wc, frwr);
> -}
> -
> -/**
> - * frwr_wc_localinv_wake - Invoked by RDMA provider for a signaled LocalInv
> WC
> - * @cq:	completion queue (ignored)
> - * @wc:	completed WR
> - *
> - * Awaken anyone waiting for an MR to finish being fenced.
> - */
> -static void
> -frwr_wc_localinv_wake(struct ib_cq *cq, struct ib_wc *wc)
> -{
> -	struct ib_cqe *cqe = wc->wr_cqe;
> -	struct rpcrdma_frwr *frwr = container_of(cqe, struct rpcrdma_frwr,
> -						 fr_cqe);
> -
> -	/* WARNING: Only wr_cqe and status are reliable at this point */
> -	if (wc->status != IB_WC_SUCCESS)
> -		frwr->fr_state = FRWR_FLUSHED_LI;
> -	trace_xprtrdma_wc_li_wake(wc, frwr);
> -	complete(&frwr->fr_linv_done);
> -}
> -
> -/**
>   * frwr_map - Register a memory region
>   * @r_xprt: controlling transport
>   * @seg: memory region co-ordinates
> @@ -378,23 +318,15 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt
> *r_xprt,
>  {
>  	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
>  	bool holes_ok = ia->ri_mrtype == IB_MR_TYPE_SG_GAPS;
> -	struct rpcrdma_frwr *frwr;
>  	struct rpcrdma_mr *mr;
>  	struct ib_mr *ibmr;
>  	struct ib_reg_wr *reg_wr;
>  	int i, n;
>  	u8 key;
>  
> -	mr = NULL;
> -	do {
> -		if (mr)
> -			rpcrdma_mr_recycle(mr);
> -		mr = rpcrdma_mr_get(r_xprt);
> -		if (!mr)
> -			goto out_getmr_err;
> -	} while (mr->frwr.fr_state != FRWR_IS_INVALID);
> -	frwr = &mr->frwr;
> -	frwr->fr_state = FRWR_IS_VALID;
> +	mr = rpcrdma_mr_get(r_xprt);
> +	if (!mr)
> +		goto out_getmr_err;
>  
>  	if (nsegs > ia->ri_max_frwr_depth)
>  		nsegs = ia->ri_max_frwr_depth;
> @@ -423,7 +355,7 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt
> *r_xprt,
>  	if (!mr->mr_nents)
>  		goto out_dmamap_err;
>  
> -	ibmr = frwr->fr_mr;
> +	ibmr = mr->frwr.fr_mr;
>  	n = ib_map_mr_sg(ibmr, mr->mr_sg, mr->mr_nents, NULL, PAGE_SIZE);
>  	if (unlikely(n != mr->mr_nents))
>  		goto out_mapmr_err;
> @@ -433,7 +365,7 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt
> *r_xprt,
>  	key = (u8)(ibmr->rkey & 0x000000FF);
>  	ib_update_fast_reg_key(ibmr, ++key);
>  
> -	reg_wr = &frwr->fr_regwr;
> +	reg_wr = &mr->frwr.fr_regwr;
>  	reg_wr->mr = ibmr;
>  	reg_wr->key = ibmr->rkey;
>  	reg_wr->access = writing ?
> @@ -465,6 +397,23 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt
> *r_xprt,
>  }
>  
>  /**
> + * frwr_wc_fastreg - Invoked by RDMA provider for a flushed FastReg WC
> + * @cq:	completion queue (ignored)
> + * @wc:	completed WR
> + *
> + */
> +static void frwr_wc_fastreg(struct ib_cq *cq, struct ib_wc *wc)
> +{
> +	struct ib_cqe *cqe = wc->wr_cqe;
> +	struct rpcrdma_frwr *frwr =
> +		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
> +
> +	/* WARNING: Only wr_cqe and status are reliable at this point */
> +	trace_xprtrdma_wc_fastreg(wc, frwr);
> +	/* The MR will get recycled when the associated req is retransmitted */
> +}
> +
> +/**
>   * frwr_send - post Send WR containing the RPC Call message
>   * @ia: interface adapter
>   * @req: Prepared RPC Call
> @@ -516,65 +465,104 @@ void frwr_reminv(struct rpcrdma_rep *rep, struct
> list_head *mrs)
>  		if (mr->mr_handle == rep->rr_inv_rkey) {
>  			list_del_init(&mr->mr_list);
>  			trace_xprtrdma_mr_remoteinv(mr);
> -			mr->frwr.fr_state = FRWR_IS_INVALID;
>  			rpcrdma_mr_unmap_and_put(mr);
>  			break;	/* only one invalidated MR per RPC */
>  		}
>  }
>  
> +static void __frwr_release_mr(struct ib_wc *wc, struct rpcrdma_mr *mr)
> +{
> +	if (wc->status != IB_WC_SUCCESS)
> +		rpcrdma_mr_recycle(mr);
> +	else
> +		rpcrdma_mr_unmap_and_put(mr);
> +}
> +
>  /**
> - * frwr_unmap_sync - invalidate memory regions that were registered for @req
> - * @r_xprt: controlling transport
> - * @mrs: list of MRs to process
> + * frwr_wc_localinv - Invoked by RDMA provider for a LOCAL_INV WC
> + * @cq:	completion queue (ignored)
> + * @wc:	completed WR
>   *
> - * Sleeps until it is safe for the host CPU to access the
> - * previously mapped memory regions.
> + */
> +static void frwr_wc_localinv(struct ib_cq *cq, struct ib_wc *wc)
> +{
> +	struct ib_cqe *cqe = wc->wr_cqe;
> +	struct rpcrdma_frwr *frwr =
> +		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
> +	struct rpcrdma_mr *mr = container_of(frwr, struct rpcrdma_mr, frwr);
> +
> +	/* WARNING: Only wr_cqe and status are reliable at this point */
> +	__frwr_release_mr(wc, mr);
> +	trace_xprtrdma_wc_li(wc, frwr);
> +}
> +
> +/**
> + * frwr_wc_localinv_wake - Invoked by RDMA provider for a LOCAL_INV WC
> + * @cq:	completion queue (ignored)
> + * @wc:	completed WR
>   *
> - * Caller ensures that @mrs is not empty before the call. This
> - * function empties the list.
> + * Awaken anyone waiting for an MR to finish being fenced.
>   */
> -void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct list_head *mrs)
> +static void frwr_wc_localinv_wake(struct ib_cq *cq, struct ib_wc *wc)
> +{
> +	struct ib_cqe *cqe = wc->wr_cqe;
> +	struct rpcrdma_frwr *frwr =
> +		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
> +	struct rpcrdma_mr *mr = container_of(frwr, struct rpcrdma_mr, frwr);
> +
> +	/* WARNING: Only wr_cqe and status are reliable at this point */
> +	__frwr_release_mr(wc, mr);
> +	trace_xprtrdma_wc_li_wake(wc, frwr);
> +	complete(&frwr->fr_linv_done);
> +}
> +
> +/**
> + * frwr_unmap_sync - invalidate memory regions that were registered for @req
> + * @r_xprt: controlling transport instance
> + * @req: rpcrdma_req with a non-empty list of MRs to process
> + *
> + * Sleeps until it is safe for the host CPU to access the previously mapped
> + * memory regions.
> + */
> +void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
>  {
>  	struct ib_send_wr *first, **prev, *last;
>  	const struct ib_send_wr *bad_wr;
> -	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
>  	struct rpcrdma_frwr *frwr;
>  	struct rpcrdma_mr *mr;
> -	int count, rc;
> +	int rc;
>  
>  	/* ORDER: Invalidate all of the MRs first
>  	 *
>  	 * Chain the LOCAL_INV Work Requests and post them with
>  	 * a single ib_post_send() call.
>  	 */
> -	frwr = NULL;
> -	count = 0;
>  	prev = &first;
> -	list_for_each_entry(mr, mrs, mr_list) {
> -		mr->frwr.fr_state = FRWR_IS_INVALID;
> +	while (!list_empty(&req->rl_registered)) {

Is this list guaranteed to always start full? Because we could potentially use
frwr uninitialized a few lines down if it's not.

net/sunrpc/xprtrdma/frwr_ops.c: In function ‘frwr_unmap_sync’:
net/sunrpc/xprtrdma/frwr_ops.c:582:3: error: ‘frwr’ may be used uninitialized in
this function [-Werror=maybe-uninitialized]
   wait_for_completion(&frwr->fr_linv_done);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Thanks,
Anna
> +		mr = rpcrdma_mr_pop(&req->rl_registered);
>  
> -		frwr = &mr->frwr;
>  		trace_xprtrdma_mr_localinv(mr);
> +		r_xprt->rx_stats.local_inv_needed++;
>  
> +		frwr = &mr->frwr;
>  		frwr->fr_cqe.done = frwr_wc_localinv;
>  		last = &frwr->fr_invwr;
> -		memset(last, 0, sizeof(*last));
> +		last->next = NULL;
>  		last->wr_cqe = &frwr->fr_cqe;
> +		last->sg_list = NULL;
> +		last->num_sge = 0;
>  		last->opcode = IB_WR_LOCAL_INV;
> +		last->send_flags = IB_SEND_SIGNALED;
>  		last->ex.invalidate_rkey = mr->mr_handle;
> -		count++;
>  
>  		*prev = last;
>  		prev = &last->next;
>  	}
> -	if (!frwr)
> -		goto unmap;
>  
>  	/* Strong send queue ordering guarantees that when the
>  	 * last WR in the chain completes, all WRs in the chain
>  	 * are complete.
>  	 */
> -	last->send_flags = IB_SEND_SIGNALED;
>  	frwr->fr_cqe.done = frwr_wc_localinv_wake;
>  	reinit_completion(&frwr->fr_linv_done);
>  
> @@ -582,26 +570,18 @@ void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct
> list_head *mrs)
>  	 * replaces the QP. The RPC reply handler won't call us
>  	 * unless ri_id->qp is a valid pointer.
>  	 */
> -	r_xprt->rx_stats.local_inv_needed++;
>  	bad_wr = NULL;
> -	rc = ib_post_send(ia->ri_id->qp, first, &bad_wr);
> -	if (bad_wr != first)
> -		wait_for_completion(&frwr->fr_linv_done);
> -	if (rc)
> -		goto out_release;
> +	rc = ib_post_send(r_xprt->rx_ia.ri_id->qp, first, &bad_wr);
> +	trace_xprtrdma_post_send(req, rc);
>  
> -	/* ORDER: Now DMA unmap all of the MRs, and return
> -	 * them to the free MR list.
> +	/* The final LOCAL_INV WR in the chain is supposed to
> +	 * do the wake. If it never gets posted, the wake will
> +	 * not happen, so don't wait in that case.
>  	 */
> -unmap:
> -	while (!list_empty(mrs)) {
> -		mr = rpcrdma_mr_pop(mrs);
> -		rpcrdma_mr_unmap_and_put(mr);
> -	}
> -	return;
> -
> -out_release:
> -	pr_err("rpcrdma: FRWR invalidate ib_post_send returned %i\n", rc);
> +	if (bad_wr != first)
> +		wait_for_completion(&frwr->fr_linv_done);
> +	if (!rc)
> +		return;
>  
>  	/* Unmap and release the MRs in the LOCAL_INV WRs that did not
>  	 * get posted.
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index 77fc1e4..6c049fd 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -1277,7 +1277,7 @@ void rpcrdma_release_rqst(struct rpcrdma_xprt *r_xprt,
> struct rpcrdma_req *req)
>  	 * RPC has relinquished all its Send Queue entries.
>  	 */
>  	if (!list_empty(&req->rl_registered))
> -		frwr_unmap_sync(r_xprt, &req->rl_registered);
> +		frwr_unmap_sync(r_xprt, req);
>  
>  	/* Ensure that any DMA mapped pages associated with
>  	 * the Send of the RPC Call have been unmapped before
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index 3c39aa3..a9de116 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -240,17 +240,9 @@ struct rpcrdma_sendctx {
>   * An external memory region is any buffer or page that is registered
>   * on the fly (ie, not pre-registered).
>   */
> -enum rpcrdma_frwr_state {
> -	FRWR_IS_INVALID,	/* ready to be used */
> -	FRWR_IS_VALID,		/* in use */
> -	FRWR_FLUSHED_FR,	/* flushed FASTREG WR */
> -	FRWR_FLUSHED_LI,	/* flushed LOCALINV WR */
> -};
> -
>  struct rpcrdma_frwr {
>  	struct ib_mr			*fr_mr;
>  	struct ib_cqe			fr_cqe;
> -	enum rpcrdma_frwr_state		fr_state;
>  	struct completion		fr_linv_done;
>  	union {
>  		struct ib_reg_wr	fr_regwr;
> @@ -567,8 +559,7 @@ struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt
> *r_xprt,
>  				struct rpcrdma_mr **mr);
>  int frwr_send(struct rpcrdma_ia *ia, struct rpcrdma_req *req);
>  void frwr_reminv(struct rpcrdma_rep *rep, struct list_head *mrs);
> -void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt,
> -		     struct list_head *mrs);
> +void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req);
>  
>  /*
>   * RPC/RDMA protocol calls - xprtrdma/rpc_rdma.c
>