SUNRPC: Generalize the RPC buffer allocation API

xprtrdma needs to allocate the Call and Reply buffers separately.
TBH, the reliance on using a single buffer for the pair of XDR
buffers is transport implementation-specific.

Transports that want to allocate separate Call and Reply buffers
will ignore the "size" argument anyway.  Don't bother passing it.

The buf_alloc method can't return two pointers. Instead, make the
method's return value an error code, and set the rq_buffer pointer
in the method itself.

This gives call_allocate an opportunity to terminate an RPC instead
of looping forever when a permanent problem occurs. If a request is
just bogus, or the transport is in a state where it can't allocate
resources for any request, there needs to be a way to kill the RPC
right there and not loop.

This immediately fixes a rare problem in the backchannel send path,
which loops if the server happens to send a CB request whose
call+reply size is larger than a page (which it shouldn't do yet).

One more issue: looks like xprt_inject_disconnect was incorrectly
placed in the failure path in call_allocate. It needs to be in the
success path, as it is for other call-sites.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/sunrpc/sched.h

@@ -239,7 +239,7 @@ struct rpc_task *rpc_wake_up_first(struct rpc_wait_queue *,
 					void *);
 void		rpc_wake_up_status(struct rpc_wait_queue *, int);
 void		rpc_delay(struct rpc_task *, unsigned long);
-void *		rpc_malloc(struct rpc_task *, size_t);
+int		rpc_malloc(struct rpc_task *);
 void		rpc_free(void *);
 int		rpciod_up(void);
 void		rpciod_down(void);

include/linux/sunrpc/xprt.h

@@ -127,7 +127,7 @@ struct rpc_xprt_ops {
 	void		(*rpcbind)(struct rpc_task *task);
 	void		(*set_port)(struct rpc_xprt *xprt, unsigned short port);
 	void		(*connect)(struct rpc_xprt *xprt, struct rpc_task *task);
-	void *		(*buf_alloc)(struct rpc_task *task, size_t size);
+	int		(*buf_alloc)(struct rpc_task *task);
 	void		(*buf_free)(void *buffer);
 	int		(*send_request)(struct rpc_task *task);
 	void		(*set_retrans_timeout)(struct rpc_task *task);

net/sunrpc/clnt.c

@@ -1691,6 +1691,7 @@ call_allocate(struct rpc_task *task)
 	struct rpc_rqst *req = task->tk_rqstp;
 	struct rpc_xprt *xprt = req->rq_xprt;
 	struct rpc_procinfo *proc = task->tk_msg.rpc_proc;
+	int status;
 
 	dprint_status(task);
 
@@ -1716,11 +1717,14 @@ call_allocate(struct rpc_task *task)
 	req->rq_rcvsize = RPC_REPHDRSIZE + slack + proc->p_replen;
 	req->rq_rcvsize <<= 2;
 
-	req->rq_buffer = xprt->ops->buf_alloc(task,
-					req->rq_callsize + req->rq_rcvsize);
-	if (req->rq_buffer != NULL)
-		return;
+	status = xprt->ops->buf_alloc(task);
 	xprt_inject_disconnect(xprt);
+	if (status == 0)
+		return;
+	if (status != -ENOMEM) {
+		rpc_exit(task, status);
+		return;
+	}
 
 	dprintk("RPC: %5u rpc_buffer allocation failed\n", task->tk_pid);
 

net/sunrpc/sched.c

@@ -849,14 +849,17 @@ static void rpc_async_schedule(struct work_struct *work)
 }
 
 /**
- * rpc_malloc - allocate an RPC buffer
- * @task: RPC task that will use this buffer
- * @size: requested byte size
+ * rpc_malloc - allocate RPC buffer resources
+ * @task: RPC task
+ *
+ * A single memory region is allocated, which is split between the
+ * RPC call and RPC reply that this task is being used for. When
+ * this RPC is retired, the memory is released by calling rpc_free.
  *
  * To prevent rpciod from hanging, this allocator never sleeps,
- * returning NULL and suppressing warning if the request cannot be serviced
- * immediately.
- * The caller can arrange to sleep in a way that is safe for rpciod.
+ * returning -ENOMEM and suppressing warning if the request cannot
+ * be serviced immediately. The caller can arrange to sleep in a
+ * way that is safe for rpciod.
  *
  * Most requests are 'small' (under 2KiB) and can be serviced from a
  * mempool, ensuring that NFS reads and writes can always proceed,
@@ -865,8 +868,10 @@ static void rpc_async_schedule(struct work_struct *work)
  * In order to avoid memory starvation triggering more writebacks of
  * NFS requests, we avoid using GFP_KERNEL.
  */
-void *rpc_malloc(struct rpc_task *task, size_t size)
+int rpc_malloc(struct rpc_task *task)
 {
+	struct rpc_rqst *rqst = task->tk_rqstp;
+	size_t size = rqst->rq_callsize + rqst->rq_rcvsize;
 	struct rpc_buffer *buf;
 	gfp_t gfp = GFP_NOIO | __GFP_NOWARN;
 
@@ -880,12 +885,13 @@ void *rpc_malloc(struct rpc_task *task, size_t size)
 		buf = kmalloc(size, gfp);
 
 	if (!buf)
-		return NULL;
+		return -ENOMEM;
 
 	buf->len = size;
 	dprintk("RPC: %5u allocated buffer of size %zu at %p\n",
 			task->tk_pid, size, buf);
-	return &buf->data;
+	rqst->rq_buffer = buf->data;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(rpc_malloc);
 

net/sunrpc/xprtrdma/svc_rdma_backchannel.c

@@ -159,29 +159,30 @@ static int svc_rdma_bc_sendto(struct svcxprt_rdma *rdma,
 /* Server-side transport endpoint wants a whole page for its send
  * buffer. The client RPC code constructs the RPC header in this
  * buffer before it invokes ->send_request.
- *
- * Returns NULL if there was a temporary allocation failure.
  */
-static void *
-xprt_rdma_bc_allocate(struct rpc_task *task, size_t size)
+static int
+xprt_rdma_bc_allocate(struct rpc_task *task)
 {
 	struct rpc_rqst *rqst = task->tk_rqstp;
 	struct svc_xprt *sxprt = rqst->rq_xprt->bc_xprt;
+	size_t size = rqst->rq_callsize;
 	struct svcxprt_rdma *rdma;
 	struct page *page;
 
 	rdma = container_of(sxprt, struct svcxprt_rdma, sc_xprt);
 
-	/* Prevent an infinite loop: try to make this case work */
-	if (size > PAGE_SIZE)
+	if (size > PAGE_SIZE) {
 		WARN_ONCE(1, "svcrdma: large bc buffer request (size %zu)\n",
 			  size);
+		return -EINVAL;
+	}
 
 	page = alloc_page(RPCRDMA_DEF_GFP);
 	if (!page)
-		return NULL;
+		return -ENOMEM;
 
-	return page_address(page);
+	rqst->rq_buffer = page_address(page);
+	return 0;
 }
 
 static void

net/sunrpc/xprtrdma/transport.c

@@ -477,7 +477,15 @@ xprt_rdma_connect(struct rpc_xprt *xprt, struct rpc_task *task)
 	}
 }
 
-/*
+/**
+ * xprt_rdma_allocate - allocate transport resources for an RPC
+ * @task: RPC task
+ *
+ * Return values:
+ *        0:	Success; rq_buffer points to RPC buffer to use
+ *   ENOMEM:	Out of memory, call again later
+ *      EIO:	A permanent error occurred, do not retry
+ *
  * The RDMA allocate/free functions need the task structure as a place
  * to hide the struct rpcrdma_req, which is necessary for the actual send/recv
  * sequence.
@@ -486,19 +494,20 @@ xprt_rdma_connect(struct rpc_xprt *xprt, struct rpc_task *task)
  * (rq_send_buf and rq_rcv_buf are both part of a single contiguous buffer).
  * We may register rq_rcv_buf when using reply chunks.
  */
-static void *
-xprt_rdma_allocate(struct rpc_task *task, size_t size)
+static int
+xprt_rdma_allocate(struct rpc_task *task)
 {
-	struct rpc_xprt *xprt = task->tk_rqstp->rq_xprt;
-	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
+	struct rpc_rqst *rqst = task->tk_rqstp;
+	size_t size = rqst->rq_callsize + rqst->rq_rcvsize;
+	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(rqst->rq_xprt);
 	struct rpcrdma_regbuf *rb;
 	struct rpcrdma_req *req;
 	size_t min_size;
 	gfp_t flags;
 
 	req = rpcrdma_buffer_get(&r_xprt->rx_buf);
 	if (req == NULL)
-		return NULL;
+		return -ENOMEM;
 
 	flags = RPCRDMA_DEF_GFP;
 	if (RPC_IS_SWAPPER(task))
@@ -515,7 +524,8 @@ xprt_rdma_allocate(struct rpc_task *task, size_t size)
 	dprintk("RPC:       %s: size %zd, request 0x%p\n", __func__, size, req);
 	req->rl_connect_cookie = 0;	/* our reserved value */
 	req->rl_task = task;
-	return req->rl_sendbuf->rg_base;
+	rqst->rq_buffer = req->rl_sendbuf->rg_base;
+	return 0;
 
 out_rdmabuf:
 	min_size = r_xprt->rx_data.inline_wsize;
@@ -558,7 +568,7 @@ xprt_rdma_allocate(struct rpc_task *task, size_t size)
 
 out_fail:
 	rpcrdma_buffer_put(req);
-	return NULL;
+	return -ENOMEM;
 }
 
 /*

net/sunrpc/xprtsock.c

@@ -2533,23 +2533,28 @@ static void xs_tcp_print_stats(struct rpc_xprt *xprt, struct seq_file *seq)
  * we allocate pages instead doing a kmalloc like rpc_malloc is because we want
  * to use the server side send routines.
  */
-static void *bc_malloc(struct rpc_task *task, size_t size)
+static int bc_malloc(struct rpc_task *task)
 {
+	struct rpc_rqst *rqst = task->tk_rqstp;
+	size_t size = rqst->rq_callsize;
 	struct page *page;
 	struct rpc_buffer *buf;
 
-	WARN_ON_ONCE(size > PAGE_SIZE - sizeof(struct rpc_buffer));
-	if (size > PAGE_SIZE - sizeof(struct rpc_buffer))
-		return NULL;
+	if (size > PAGE_SIZE - sizeof(struct rpc_buffer)) {
+		WARN_ONCE(1, "xprtsock: large bc buffer request (size %zu)\n",
+			  size);
+		return -EINVAL;
+	}
 
 	page = alloc_page(GFP_KERNEL);
 	if (!page)
-		return NULL;
+		return -ENOMEM;
 
 	buf = page_address(page);
 	buf->len = PAGE_SIZE;
 
-	return buf->data;
+	rqst->rq_buffer = buf->data;
+	return 0;
 }
 
 /*