backchannel_rqst.c

// SPDX-License-Identifier: GPL-2.0-only
/******************************************************************************

(c) 2007 Network Appliance, Inc.  All Rights Reserved.
(c) 2009 NetApp.  All Rights Reserved.


******************************************************************************/

#include <linux/tcp.h>
#include <linux/slab.h>
#include <linux/sunrpc/xprt.h>
#include <linux/export.h>
#include <linux/sunrpc/bc_xprt.h>

#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
#define RPCDBG_FACILITY	RPCDBG_TRANS
#endif

#define BC_MAX_SLOTS	64U

unsigned int xprt_bc_max_slots(struct rpc_xprt *xprt)
{
	return BC_MAX_SLOTS;
}

/*
 * Helper routines that track the number of preallocation elements
 * on the transport.
 */
static inline int xprt_need_to_requeue(struct rpc_xprt *xprt)
{
	return xprt->bc_alloc_count < xprt->bc_alloc_max;
}

/*
 * Free the preallocated rpc_rqst structure and the memory
 * buffers hanging off of it.
 */
static void xprt_free_allocation(struct rpc_rqst *req)
{
	struct xdr_buf *xbufp;

	dprintk("RPC:        free allocations for req= %p\n", req);
	WARN_ON_ONCE(test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));
	xbufp = &req->rq_rcv_buf;
	free_page((unsigned long)xbufp->head[0].iov_base);
	xbufp = &req->rq_snd_buf;
	free_page((unsigned long)xbufp->head[0].iov_base);
	kfree(req);
}

static void xprt_bc_reinit_xdr_buf(struct xdr_buf *buf)
{
	buf->head[0].iov_len = PAGE_SIZE;
	buf->tail[0].iov_len = 0;
	buf->pages = NULL;
	buf->page_len = 0;
	buf->flags = 0;
	buf->len = 0;
	buf->buflen = PAGE_SIZE;
}

static int xprt_alloc_xdr_buf(struct xdr_buf *buf, gfp_t gfp_flags)
{
	struct page *page;
	/* Preallocate one XDR receive buffer */
	page = alloc_page(gfp_flags);
	if (page == NULL)
		return -ENOMEM;
	xdr_buf_init(buf, page_address(page), PAGE_SIZE);
	return 0;
}

static struct rpc_rqst *xprt_alloc_bc_req(struct rpc_xprt *xprt)
{
	gfp_t gfp_flags = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
	struct rpc_rqst *req;

	/* Pre-allocate one backchannel rpc_rqst */
	req = kzalloc(sizeof(*req), gfp_flags);
	if (req == NULL)
		return NULL;

	req->rq_xprt = xprt;

	/* Preallocate one XDR receive buffer */
	if (xprt_alloc_xdr_buf(&req->rq_rcv_buf, gfp_flags) < 0) {
		printk(KERN_ERR "Failed to create bc receive xbuf\n");
		goto out_free;
	}
	req->rq_rcv_buf.len = PAGE_SIZE;

	/* Preallocate one XDR send buffer */
	if (xprt_alloc_xdr_buf(&req->rq_snd_buf, gfp_flags) < 0) {
		printk(KERN_ERR "Failed to create bc snd xbuf\n");
		goto out_free;
	}
	return req;
out_free:
	xprt_free_allocation(req);
	return NULL;
}

/*
 * Preallocate up to min_reqs structures and related buffers for use
 * by the backchannel.  This function can be called multiple times
 * when creating new sessions that use the same rpc_xprt.  The
 * preallocated buffers are added to the pool of resources used by
 * the rpc_xprt.  Any one of these resources may be used by an
 * incoming callback request.  It's up to the higher levels in the
 * stack to enforce that the maximum number of session slots is not
 * being exceeded.
 *
 * Some callback arguments can be large.  For example, a pNFS server
 * using multiple deviceids.  The list can be unbound, but the client
 * has the ability to tell the server the maximum size of the callback
 * requests.  Each deviceID is 16 bytes, so allocate one page
 * for the arguments to have enough room to receive a number of these
 * deviceIDs.  The NFS client indicates to the pNFS server that its
 * callback requests can be up to 4096 bytes in size.
 */
int xprt_setup_backchannel(struct rpc_xprt *xprt, unsigned int min_reqs)
{
	if (!xprt->ops->bc_setup)
		return 0;
	return xprt->ops->bc_setup(xprt, min_reqs);
}
EXPORT_SYMBOL_GPL(xprt_setup_backchannel);

int xprt_setup_bc(struct rpc_xprt *xprt, unsigned int min_reqs)
{
	struct rpc_rqst *req;
	struct list_head tmp_list;
	int i;

	dprintk("RPC:       setup backchannel transport\n");

	if (min_reqs > BC_MAX_SLOTS)
		min_reqs = BC_MAX_SLOTS;

	/*
	 * We use a temporary list to keep track of the preallocated
	 * buffers.  Once we're done building the list we splice it
	 * into the backchannel preallocation list off of the rpc_xprt
	 * struct.  This helps minimize the amount of time the list
	 * lock is held on the rpc_xprt struct.  It also makes cleanup
	 * easier in case of memory allocation errors.
	 */
	INIT_LIST_HEAD(&tmp_list);
	for (i = 0; i < min_reqs; i++) {
		/* Pre-allocate one backchannel rpc_rqst */
		req = xprt_alloc_bc_req(xprt);
		if (req == NULL) {
			printk(KERN_ERR "Failed to create bc rpc_rqst\n");
			goto out_free;
		}

		/* Add the allocated buffer to the tmp list */
		dprintk("RPC:       adding req= %p\n", req);
		list_add(&req->rq_bc_pa_list, &tmp_list);
	}

	/*
	 * Add the temporary list to the backchannel preallocation list
	 */
	spin_lock(&xprt->bc_pa_lock);
	list_splice(&tmp_list, &xprt->bc_pa_list);
	xprt->bc_alloc_count += min_reqs;
	xprt->bc_alloc_max += min_reqs;
	atomic_add(min_reqs, &xprt->bc_slot_count);
	spin_unlock(&xprt->bc_pa_lock);

	dprintk("RPC:       setup backchannel transport done\n");
	return 0;

out_free:
	/*
	 * Memory allocation failed, free the temporary list
	 */
	while (!list_empty(&tmp_list)) {
		req = list_first_entry(&tmp_list,
				struct rpc_rqst,
				rq_bc_pa_list);
		list_del(&req->rq_bc_pa_list);
		xprt_free_allocation(req);
	}

	dprintk("RPC:       setup backchannel transport failed\n");
	return -ENOMEM;
}

/**
 * xprt_destroy_backchannel - Destroys the backchannel preallocated structures.
 * @xprt:	the transport holding the preallocated strucures
 * @max_reqs:	the maximum number of preallocated structures to destroy
 *
 * Since these structures may have been allocated by multiple calls
 * to xprt_setup_backchannel, we only destroy up to the maximum number
 * of reqs specified by the caller.
 */
void xprt_destroy_backchannel(struct rpc_xprt *xprt, unsigned int max_reqs)
{
	if (xprt->ops->bc_destroy)
		xprt->ops->bc_destroy(xprt, max_reqs);
}
EXPORT_SYMBOL_GPL(xprt_destroy_backchannel);

void xprt_destroy_bc(struct rpc_xprt *xprt, unsigned int max_reqs)
{
	struct rpc_rqst *req = NULL, *tmp = NULL;

	dprintk("RPC:        destroy backchannel transport\n");

	if (max_reqs == 0)
		goto out;

	spin_lock_bh(&xprt->bc_pa_lock);
	xprt->bc_alloc_max -= min(max_reqs, xprt->bc_alloc_max);
	list_for_each_entry_safe(req, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
		dprintk("RPC:        req=%p\n", req);
		list_del(&req->rq_bc_pa_list);
		xprt_free_allocation(req);
		xprt->bc_alloc_count--;
		atomic_dec(&xprt->bc_slot_count);
		if (--max_reqs == 0)
			break;
	}
	spin_unlock_bh(&xprt->bc_pa_lock);

out:
	dprintk("RPC:        backchannel list empty= %s\n",
		list_empty(&xprt->bc_pa_list) ? "true" : "false");
}

static struct rpc_rqst *xprt_get_bc_request(struct rpc_xprt *xprt, __be32 xid,
		struct rpc_rqst *new)
{
	struct rpc_rqst *req = NULL;

	dprintk("RPC:       allocate a backchannel request\n");
	if (list_empty(&xprt->bc_pa_list)) {
		if (!new)
			goto not_found;
		if (atomic_read(&xprt->bc_slot_count) >= BC_MAX_SLOTS)
			goto not_found;
		list_add_tail(&new->rq_bc_pa_list, &xprt->bc_pa_list);
		xprt->bc_alloc_count++;
		atomic_inc(&xprt->bc_slot_count);
	}
	req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
				rq_bc_pa_list);
	req->rq_reply_bytes_recvd = 0;
	memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
			sizeof(req->rq_private_buf));
	req->rq_xid = xid;
	req->rq_connect_cookie = xprt->connect_cookie;
	dprintk("RPC:       backchannel req=%p\n", req);
not_found:
	return req;
}

/*
 * Return the preallocated rpc_rqst structure and XDR buffers
 * associated with this rpc_task.
 */
void xprt_free_bc_request(struct rpc_rqst *req)
{
	struct rpc_xprt *xprt = req->rq_xprt;

	xprt->ops->bc_free_rqst(req);
}

void xprt_free_bc_rqst(struct rpc_rqst *req)
{
	struct rpc_xprt *xprt = req->rq_xprt;

	dprintk("RPC:       free backchannel req=%p\n", req);

	req->rq_connect_cookie = xprt->connect_cookie - 1;
	smp_mb__before_atomic();
	clear_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
	smp_mb__after_atomic();

	/*
	 * Return it to the list of preallocations so that it
	 * may be reused by a new callback request.
	 */
	spin_lock_bh(&xprt->bc_pa_lock);
	if (xprt_need_to_requeue(xprt)) {
		xprt_bc_reinit_xdr_buf(&req->rq_snd_buf);
		xprt_bc_reinit_xdr_buf(&req->rq_rcv_buf);
		req->rq_rcv_buf.len = PAGE_SIZE;
		list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
		xprt->bc_alloc_count++;
		atomic_inc(&xprt->bc_slot_count);
		req = NULL;
	}
	spin_unlock_bh(&xprt->bc_pa_lock);
	if (req != NULL) {
		/*
		 * The last remaining session was destroyed while this
		 * entry was in use.  Free the entry and don't attempt
		 * to add back to the list because there is no need to
		 * have anymore preallocated entries.
		 */
		dprintk("RPC:       Last session removed req=%p\n", req);
		xprt_free_allocation(req);
	}
	xprt_put(xprt);
}

/*
 * One or more rpc_rqst structure have been preallocated during the
 * backchannel setup.  Buffer space for the send and private XDR buffers
 * has been preallocated as well.  Use xprt_alloc_bc_request to allocate
 * to this request.  Use xprt_free_bc_request to return it.
 *
 * We know that we're called in soft interrupt context, grab the spin_lock
 * since there is no need to grab the bottom half spin_lock.
 *
 * Return an available rpc_rqst, otherwise NULL if non are available.
 */
struct rpc_rqst *xprt_lookup_bc_request(struct rpc_xprt *xprt, __be32 xid)
{
	struct rpc_rqst *req, *new = NULL;

	do {
		spin_lock(&xprt->bc_pa_lock);
		list_for_each_entry(req, &xprt->bc_pa_list, rq_bc_pa_list) {
			if (req->rq_connect_cookie != xprt->connect_cookie)
				continue;
			if (req->rq_xid == xid)
				goto found;
		}
		req = xprt_get_bc_request(xprt, xid, new);
found:
		spin_unlock(&xprt->bc_pa_lock);
		if (new) {
			if (req != new)
				xprt_free_allocation(new);
			break;
		} else if (req)
			break;
		new = xprt_alloc_bc_req(xprt);
	} while (new);
	return req;
}

/*
 * Add callback request to callback list.  Wake a thread
 * on the first pool (usually the only pool) to handle it.
 */
void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
{
	struct rpc_xprt *xprt = req->rq_xprt;
	struct svc_serv *bc_serv = xprt->bc_serv;

	spin_lock(&xprt->bc_pa_lock);
	list_del(&req->rq_bc_pa_list);
	xprt->bc_alloc_count--;
	spin_unlock(&xprt->bc_pa_lock);

	req->rq_private_buf.len = copied;
	set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);

	dprintk("RPC:       add callback request to list\n");
	xprt_get(xprt);
	lwq_enqueue(&req->rq_bc_list, &bc_serv->sv_cb_list);
	svc_pool_wake_idle_thread(&bc_serv->sv_pools[0]);
}