Re: [PATCH v1 10/13] xprtrdma: Release FRMR segment buffers during LOCAL_INV completion

[Shirley Ma <shirley.ma-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

Would it be possible to delay rpcrdma_buffer_put() until LOCAL_INV request send completion? remove rpcrdma_buffer_put() from xprt_rdma_free(), add a call back after LOCAL_INV completed?

Shirley

On 06/23/2014 03:40 PM, Chuck Lever wrote:
> FRMR uses a LOCAL_INV Work Request, which is asynchronous, to
> deregister segment buffers.  Other registration strategies use
> synchronous deregistration mechanisms (like ib_unmap_fmr()).
> 
> For a synchronous deregistration mechanism, it makes sense for
> xprt_rdma_free() to put segment buffers back into the buffer pool
> immediately once rpcrdma_deregister_external() returns.
> 
> This is currently also what FRMR is doing. It is releasing segment
> buffers just after the LOCAL_INV WR is posted.
> 
> But segment buffers need to be put back after the LOCAL_INV WR
> _completes_ (or flushes). Otherwise, rpcrdma_buffer_get() can then
> assign these segment buffers to another RPC task while they are
> still "in use" by the hardware.
> 
> The result of re-using an FRMR too quickly is that it's rkey
> no longer matches the rkey that was registered with the provider.
> This results in FAST_REG_MR or LOCAL_INV Work Requests completing
> with IB_WC_MW_BIND_ERR, and the FRMR, and thus the transport,
> becomes unusable.
> 
> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
>  net/sunrpc/xprtrdma/verbs.c     |   44 +++++++++++++++++++++++++++++++++++----
>  net/sunrpc/xprtrdma/xprt_rdma.h |    2 ++
>  2 files changed, 42 insertions(+), 4 deletions(-)
> 
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index f24f0bf..52f57f7 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -62,6 +62,8 @@
>  #endif
>  
>  static void rpcrdma_decrement_frmr_rkey(struct rpcrdma_mw *);
> +static void rpcrdma_get_mw(struct rpcrdma_mw *);
> +static void rpcrdma_put_mw(struct rpcrdma_mw *);
>  
>  /*
>   * internal functions
> @@ -167,6 +169,7 @@ rpcrdma_sendcq_process_wc(struct ib_wc *wc)
>  		if (fastreg)
>  			rpcrdma_decrement_frmr_rkey(mw);
>  	}
> +	rpcrdma_put_mw(mw);
>  }
>  
>  static int
> @@ -1034,7 +1037,7 @@ rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
>  	len += cdata->padding;
>  	switch (ia->ri_memreg_strategy) {
>  	case RPCRDMA_FRMR:
> -		len += buf->rb_max_requests * RPCRDMA_MAX_SEGS *
> +		len += (buf->rb_max_requests + 1) * RPCRDMA_MAX_SEGS *
>  				sizeof(struct rpcrdma_mw);
>  		break;
>  	case RPCRDMA_MTHCAFMR:
> @@ -1076,7 +1079,7 @@ rpcrdma_buffer_create(struct rpcrdma_buffer *buf, struct rpcrdma_ep *ep,
>  	r = (struct rpcrdma_mw *)p;
>  	switch (ia->ri_memreg_strategy) {
>  	case RPCRDMA_FRMR:
> -		for (i = buf->rb_max_requests * RPCRDMA_MAX_SEGS; i; i--) {
> +		for (i = (buf->rb_max_requests+1) * RPCRDMA_MAX_SEGS; i; i--) {
>  			r->r.frmr.fr_mr = ib_alloc_fast_reg_mr(ia->ri_pd,
>  						ia->ri_max_frmr_depth);
>  			if (IS_ERR(r->r.frmr.fr_mr)) {
> @@ -1252,12 +1255,36 @@ rpcrdma_buffer_destroy(struct rpcrdma_buffer *buf)
>  }
>  
>  static void
> -rpcrdma_put_mw_locked(struct rpcrdma_mw *mw)
> +rpcrdma_free_mw(struct kref *kref)
>  {
> +	struct rpcrdma_mw *mw = container_of(kref, struct rpcrdma_mw, mw_ref);
>  	list_add_tail(&mw->mw_list, &mw->mw_pool->rb_mws);
>  }
>  
>  static void
> +rpcrdma_put_mw_locked(struct rpcrdma_mw *mw)
> +{
> +	kref_put(&mw->mw_ref, rpcrdma_free_mw);
> +}
> +
> +static void
> +rpcrdma_get_mw(struct rpcrdma_mw *mw)
> +{
> +	kref_get(&mw->mw_ref);
> +}
> +
> +static void
> +rpcrdma_put_mw(struct rpcrdma_mw *mw)
> +{
> +	struct rpcrdma_buffer *buffers = mw->mw_pool;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&buffers->rb_lock, flags);
> +	rpcrdma_put_mw_locked(mw);
> +	spin_unlock_irqrestore(&buffers->rb_lock, flags);
> +}
> +
> +static void
>  rpcrdma_buffer_put_mw(struct rpcrdma_mw **mw)
>  {
>  	rpcrdma_put_mw_locked(*mw);
> @@ -1304,6 +1331,7 @@ rpcrdma_buffer_get_mws(struct rpcrdma_req *req, struct rpcrdma_buffer *buffers)
>  		r = list_entry(buffers->rb_mws.next,
>  				struct rpcrdma_mw, mw_list);
>  		list_del(&r->mw_list);
> +		kref_init(&r->mw_ref);
>  		r->mw_pool = buffers;
>  		req->rl_segments[i].mr_chunk.rl_mw = r;
>  	}
> @@ -1583,6 +1611,7 @@ rpcrdma_register_frmr_external(struct rpcrdma_mr_seg *seg,
>  	dprintk("RPC:       %s: Using frmr %p to map %d segments\n",
>  		__func__, seg1->mr_chunk.rl_mw, i);
>  
> +	rpcrdma_get_mw(seg1->mr_chunk.rl_mw);
>  	if (unlikely(seg1->mr_chunk.rl_mw->r.frmr.fr_state == FRMR_IS_VALID)) {
>  		dprintk("RPC:       %s: frmr %x left valid, posting invalidate.\n",
>  			__func__,
> @@ -1595,6 +1624,7 @@ rpcrdma_register_frmr_external(struct rpcrdma_mr_seg *seg,
>  		invalidate_wr.send_flags = IB_SEND_SIGNALED;
>  		invalidate_wr.ex.invalidate_rkey =
>  			seg1->mr_chunk.rl_mw->r.frmr.fr_mr->rkey;
> +		rpcrdma_get_mw(seg1->mr_chunk.rl_mw);
>  		DECR_CQCOUNT(&r_xprt->rx_ep);
>  		post_wr = &invalidate_wr;
>  	} else
> @@ -1638,6 +1668,9 @@ rpcrdma_register_frmr_external(struct rpcrdma_mr_seg *seg,
>  	*nsegs = i;
>  	return 0;
>  out_err:
> +	rpcrdma_put_mw(seg1->mr_chunk.rl_mw);
> +	if (post_wr == &invalidate_wr)
> +		rpcrdma_put_mw(seg1->mr_chunk.rl_mw);
>  	while (i--)
>  		rpcrdma_unmap_one(ia, --seg);
>  	return rc;
> @@ -1653,6 +1686,7 @@ rpcrdma_deregister_frmr_external(struct rpcrdma_mr_seg *seg,
>  
>  	while (seg1->mr_nsegs--)
>  		rpcrdma_unmap_one(ia, seg++);
> +	rpcrdma_get_mw(seg1->mr_chunk.rl_mw);
>  
>  	memset(&invalidate_wr, 0, sizeof invalidate_wr);
>  	invalidate_wr.wr_id = (unsigned long)(void *)seg1->mr_chunk.rl_mw;
> @@ -1664,9 +1698,11 @@ rpcrdma_deregister_frmr_external(struct rpcrdma_mr_seg *seg,
>  	read_lock(&ia->ri_qplock);
>  	rc = ib_post_send(ia->ri_id->qp, &invalidate_wr, &bad_wr);
>  	read_unlock(&ia->ri_qplock);
> -	if (rc)
> +	if (rc) {
> +		rpcrdma_put_mw(seg1->mr_chunk.rl_mw);
>  		dprintk("RPC:       %s: failed ib_post_send for invalidate,"
>  			" status %i\n", __func__, rc);
> +	}
>  	return rc;
>  }
>  
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index b81e5b5..7a140fe 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -44,6 +44,7 @@
>  #include <linux/spinlock.h> 		/* spinlock_t, etc */
>  #include <linux/atomic.h>			/* atomic_t, etc */
>  #include <linux/workqueue.h>		/* struct work_struct */
> +#include <linux/kref.h>
>  
>  #include <rdma/rdma_cm.h>		/* RDMA connection api */
>  #include <rdma/ib_verbs.h>		/* RDMA verbs api */
> @@ -176,6 +177,7 @@ struct rpcrdma_mw {
>  	} r;
>  	struct list_head	mw_list;
>  	struct rpcrdma_buffer	*mw_pool;
> +	struct kref		mw_ref;
>  };
>  
>  #define RPCRDMA_BIT_FASTREG		(0)
> 
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