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1// SPDX-License-Identifier: GPL-2.0-only
2/******************************************************************************
3
4(c) 2007 Network Appliance, Inc. All Rights Reserved.
5(c) 2009 NetApp. All Rights Reserved.
6
7
8******************************************************************************/
9
10#include <linux/tcp.h>
11#include <linux/slab.h>
12#include <linux/sunrpc/xprt.h>
13#include <linux/export.h>
14#include <linux/sunrpc/bc_xprt.h>
15
16#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
17#define RPCDBG_FACILITY RPCDBG_TRANS
18#endif
19
20#define BC_MAX_SLOTS 64U
21
22unsigned int xprt_bc_max_slots(struct rpc_xprt *xprt)
23{
24 return BC_MAX_SLOTS;
25}
26
27/*
28 * Helper routines that track the number of preallocation elements
29 * on the transport.
30 */
31static inline int xprt_need_to_requeue(struct rpc_xprt *xprt)
32{
33 return xprt->bc_alloc_count < xprt->bc_alloc_max;
34}
35
36/*
37 * Free the preallocated rpc_rqst structure and the memory
38 * buffers hanging off of it.
39 */
40static void xprt_free_allocation(struct rpc_rqst *req)
41{
42 struct xdr_buf *xbufp;
43
44 dprintk("RPC: free allocations for req= %p\n", req);
45 WARN_ON_ONCE(test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));
46 xbufp = &req->rq_rcv_buf;
47 free_page((unsigned long)xbufp->head[0].iov_base);
48 xbufp = &req->rq_snd_buf;
49 free_page((unsigned long)xbufp->head[0].iov_base);
50 kfree(req);
51}
52
53static void xprt_bc_reinit_xdr_buf(struct xdr_buf *buf)
54{
55 buf->head[0].iov_len = PAGE_SIZE;
56 buf->tail[0].iov_len = 0;
57 buf->pages = NULL;
58 buf->page_len = 0;
59 buf->flags = 0;
60 buf->len = 0;
61 buf->buflen = PAGE_SIZE;
62}
63
64static int xprt_alloc_xdr_buf(struct xdr_buf *buf, gfp_t gfp_flags)
65{
66 struct page *page;
67 /* Preallocate one XDR receive buffer */
68 page = alloc_page(gfp_flags);
69 if (page == NULL)
70 return -ENOMEM;
71 xdr_buf_init(buf, page_address(page), PAGE_SIZE);
72 return 0;
73}
74
75static struct rpc_rqst *xprt_alloc_bc_req(struct rpc_xprt *xprt)
76{
77 gfp_t gfp_flags = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
78 struct rpc_rqst *req;
79
80 /* Pre-allocate one backchannel rpc_rqst */
81 req = kzalloc(sizeof(*req), gfp_flags);
82 if (req == NULL)
83 return NULL;
84
85 req->rq_xprt = xprt;
86
87 /* Preallocate one XDR receive buffer */
88 if (xprt_alloc_xdr_buf(&req->rq_rcv_buf, gfp_flags) < 0) {
89 printk(KERN_ERR "Failed to create bc receive xbuf\n");
90 goto out_free;
91 }
92 req->rq_rcv_buf.len = PAGE_SIZE;
93
94 /* Preallocate one XDR send buffer */
95 if (xprt_alloc_xdr_buf(&req->rq_snd_buf, gfp_flags) < 0) {
96 printk(KERN_ERR "Failed to create bc snd xbuf\n");
97 goto out_free;
98 }
99 return req;
100out_free:
101 xprt_free_allocation(req);
102 return NULL;
103}
104
105/*
106 * Preallocate up to min_reqs structures and related buffers for use
107 * by the backchannel. This function can be called multiple times
108 * when creating new sessions that use the same rpc_xprt. The
109 * preallocated buffers are added to the pool of resources used by
110 * the rpc_xprt. Any one of these resources may be used by an
111 * incoming callback request. It's up to the higher levels in the
112 * stack to enforce that the maximum number of session slots is not
113 * being exceeded.
114 *
115 * Some callback arguments can be large. For example, a pNFS server
116 * using multiple deviceids. The list can be unbound, but the client
117 * has the ability to tell the server the maximum size of the callback
118 * requests. Each deviceID is 16 bytes, so allocate one page
119 * for the arguments to have enough room to receive a number of these
120 * deviceIDs. The NFS client indicates to the pNFS server that its
121 * callback requests can be up to 4096 bytes in size.
122 */
123int xprt_setup_backchannel(struct rpc_xprt *xprt, unsigned int min_reqs)
124{
125 if (!xprt->ops->bc_setup)
126 return 0;
127 return xprt->ops->bc_setup(xprt, min_reqs);
128}
129EXPORT_SYMBOL_GPL(xprt_setup_backchannel);
130
131int xprt_setup_bc(struct rpc_xprt *xprt, unsigned int min_reqs)
132{
133 struct rpc_rqst *req;
134 struct list_head tmp_list;
135 int i;
136
137 dprintk("RPC: setup backchannel transport\n");
138
139 if (min_reqs > BC_MAX_SLOTS)
140 min_reqs = BC_MAX_SLOTS;
141
142 /*
143 * We use a temporary list to keep track of the preallocated
144 * buffers. Once we're done building the list we splice it
145 * into the backchannel preallocation list off of the rpc_xprt
146 * struct. This helps minimize the amount of time the list
147 * lock is held on the rpc_xprt struct. It also makes cleanup
148 * easier in case of memory allocation errors.
149 */
150 INIT_LIST_HEAD(&tmp_list);
151 for (i = 0; i < min_reqs; i++) {
152 /* Pre-allocate one backchannel rpc_rqst */
153 req = xprt_alloc_bc_req(xprt);
154 if (req == NULL) {
155 printk(KERN_ERR "Failed to create bc rpc_rqst\n");
156 goto out_free;
157 }
158
159 /* Add the allocated buffer to the tmp list */
160 dprintk("RPC: adding req= %p\n", req);
161 list_add(&req->rq_bc_pa_list, &tmp_list);
162 }
163
164 /*
165 * Add the temporary list to the backchannel preallocation list
166 */
167 spin_lock(&xprt->bc_pa_lock);
168 list_splice(&tmp_list, &xprt->bc_pa_list);
169 xprt->bc_alloc_count += min_reqs;
170 xprt->bc_alloc_max += min_reqs;
171 atomic_add(min_reqs, &xprt->bc_slot_count);
172 spin_unlock(&xprt->bc_pa_lock);
173
174 dprintk("RPC: setup backchannel transport done\n");
175 return 0;
176
177out_free:
178 /*
179 * Memory allocation failed, free the temporary list
180 */
181 while (!list_empty(&tmp_list)) {
182 req = list_first_entry(&tmp_list,
183 struct rpc_rqst,
184 rq_bc_pa_list);
185 list_del(&req->rq_bc_pa_list);
186 xprt_free_allocation(req);
187 }
188
189 dprintk("RPC: setup backchannel transport failed\n");
190 return -ENOMEM;
191}
192
193/**
194 * xprt_destroy_backchannel - Destroys the backchannel preallocated structures.
195 * @xprt: the transport holding the preallocated strucures
196 * @max_reqs: the maximum number of preallocated structures to destroy
197 *
198 * Since these structures may have been allocated by multiple calls
199 * to xprt_setup_backchannel, we only destroy up to the maximum number
200 * of reqs specified by the caller.
201 */
202void xprt_destroy_backchannel(struct rpc_xprt *xprt, unsigned int max_reqs)
203{
204 if (xprt->ops->bc_destroy)
205 xprt->ops->bc_destroy(xprt, max_reqs);
206}
207EXPORT_SYMBOL_GPL(xprt_destroy_backchannel);
208
209void xprt_destroy_bc(struct rpc_xprt *xprt, unsigned int max_reqs)
210{
211 struct rpc_rqst *req = NULL, *tmp = NULL;
212
213 dprintk("RPC: destroy backchannel transport\n");
214
215 if (max_reqs == 0)
216 goto out;
217
218 spin_lock_bh(&xprt->bc_pa_lock);
219 xprt->bc_alloc_max -= min(max_reqs, xprt->bc_alloc_max);
220 list_for_each_entry_safe(req, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
221 dprintk("RPC: req=%p\n", req);
222 list_del(&req->rq_bc_pa_list);
223 xprt_free_allocation(req);
224 xprt->bc_alloc_count--;
225 atomic_dec(&xprt->bc_slot_count);
226 if (--max_reqs == 0)
227 break;
228 }
229 spin_unlock_bh(&xprt->bc_pa_lock);
230
231out:
232 dprintk("RPC: backchannel list empty= %s\n",
233 list_empty(&xprt->bc_pa_list) ? "true" : "false");
234}
235
236static struct rpc_rqst *xprt_get_bc_request(struct rpc_xprt *xprt, __be32 xid,
237 struct rpc_rqst *new)
238{
239 struct rpc_rqst *req = NULL;
240
241 dprintk("RPC: allocate a backchannel request\n");
242 if (list_empty(&xprt->bc_pa_list)) {
243 if (!new)
244 goto not_found;
245 if (atomic_read(&xprt->bc_slot_count) >= BC_MAX_SLOTS)
246 goto not_found;
247 list_add_tail(&new->rq_bc_pa_list, &xprt->bc_pa_list);
248 xprt->bc_alloc_count++;
249 atomic_inc(&xprt->bc_slot_count);
250 }
251 req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
252 rq_bc_pa_list);
253 req->rq_reply_bytes_recvd = 0;
254 memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
255 sizeof(req->rq_private_buf));
256 req->rq_xid = xid;
257 req->rq_connect_cookie = xprt->connect_cookie;
258 dprintk("RPC: backchannel req=%p\n", req);
259not_found:
260 return req;
261}
262
263/*
264 * Return the preallocated rpc_rqst structure and XDR buffers
265 * associated with this rpc_task.
266 */
267void xprt_free_bc_request(struct rpc_rqst *req)
268{
269 struct rpc_xprt *xprt = req->rq_xprt;
270
271 xprt->ops->bc_free_rqst(req);
272}
273
274void xprt_free_bc_rqst(struct rpc_rqst *req)
275{
276 struct rpc_xprt *xprt = req->rq_xprt;
277
278 dprintk("RPC: free backchannel req=%p\n", req);
279
280 req->rq_connect_cookie = xprt->connect_cookie - 1;
281 smp_mb__before_atomic();
282 clear_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
283 smp_mb__after_atomic();
284
285 /*
286 * Return it to the list of preallocations so that it
287 * may be reused by a new callback request.
288 */
289 spin_lock_bh(&xprt->bc_pa_lock);
290 if (xprt_need_to_requeue(xprt)) {
291 xprt_bc_reinit_xdr_buf(&req->rq_snd_buf);
292 xprt_bc_reinit_xdr_buf(&req->rq_rcv_buf);
293 req->rq_rcv_buf.len = PAGE_SIZE;
294 list_add_tail(&req->rq_bc_pa_list, &xprt->bc_pa_list);
295 xprt->bc_alloc_count++;
296 atomic_inc(&xprt->bc_slot_count);
297 req = NULL;
298 }
299 spin_unlock_bh(&xprt->bc_pa_lock);
300 if (req != NULL) {
301 /*
302 * The last remaining session was destroyed while this
303 * entry was in use. Free the entry and don't attempt
304 * to add back to the list because there is no need to
305 * have anymore preallocated entries.
306 */
307 dprintk("RPC: Last session removed req=%p\n", req);
308 xprt_free_allocation(req);
309 }
310 xprt_put(xprt);
311}
312
313/*
314 * One or more rpc_rqst structure have been preallocated during the
315 * backchannel setup. Buffer space for the send and private XDR buffers
316 * has been preallocated as well. Use xprt_alloc_bc_request to allocate
317 * to this request. Use xprt_free_bc_request to return it.
318 *
319 * We know that we're called in soft interrupt context, grab the spin_lock
320 * since there is no need to grab the bottom half spin_lock.
321 *
322 * Return an available rpc_rqst, otherwise NULL if non are available.
323 */
324struct rpc_rqst *xprt_lookup_bc_request(struct rpc_xprt *xprt, __be32 xid)
325{
326 struct rpc_rqst *req, *new = NULL;
327
328 do {
329 spin_lock(&xprt->bc_pa_lock);
330 list_for_each_entry(req, &xprt->bc_pa_list, rq_bc_pa_list) {
331 if (req->rq_connect_cookie != xprt->connect_cookie)
332 continue;
333 if (req->rq_xid == xid)
334 goto found;
335 }
336 req = xprt_get_bc_request(xprt, xid, new);
337found:
338 spin_unlock(&xprt->bc_pa_lock);
339 if (new) {
340 if (req != new)
341 xprt_free_allocation(new);
342 break;
343 } else if (req)
344 break;
345 new = xprt_alloc_bc_req(xprt);
346 } while (new);
347 return req;
348}
349
350/*
351 * Add callback request to callback list. Wake a thread
352 * on the first pool (usually the only pool) to handle it.
353 */
354void xprt_complete_bc_request(struct rpc_rqst *req, uint32_t copied)
355{
356 struct rpc_xprt *xprt = req->rq_xprt;
357 struct svc_serv *bc_serv = xprt->bc_serv;
358
359 spin_lock(&xprt->bc_pa_lock);
360 list_del(&req->rq_bc_pa_list);
361 xprt->bc_alloc_count--;
362 spin_unlock(&xprt->bc_pa_lock);
363
364 req->rq_private_buf.len = copied;
365 set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
366
367 dprintk("RPC: add callback request to list\n");
368 xprt_get(xprt);
369 lwq_enqueue(&req->rq_bc_list, &bc_serv->sv_cb_list);
370 svc_pool_wake_idle_thread(&bc_serv->sv_pools[0]);
371}
1/******************************************************************************
2
3(c) 2007 Network Appliance, Inc. All Rights Reserved.
4(c) 2009 NetApp. All Rights Reserved.
5
6NetApp provides this source code under the GPL v2 License.
7The GPL v2 license is available at
8http://opensource.org/licenses/gpl-license.php.
9
10THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
11"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
12LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
13A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
14CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
15EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
16PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
17PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
18LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
19NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
20SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
21
22******************************************************************************/
23
24#include <linux/tcp.h>
25#include <linux/slab.h>
26#include <linux/sunrpc/xprt.h>
27
28#ifdef RPC_DEBUG
29#define RPCDBG_FACILITY RPCDBG_TRANS
30#endif
31
32/*
33 * Helper routines that track the number of preallocation elements
34 * on the transport.
35 */
36static inline int xprt_need_to_requeue(struct rpc_xprt *xprt)
37{
38 return xprt->bc_alloc_count > 0;
39}
40
41static inline void xprt_inc_alloc_count(struct rpc_xprt *xprt, unsigned int n)
42{
43 xprt->bc_alloc_count += n;
44}
45
46static inline int xprt_dec_alloc_count(struct rpc_xprt *xprt, unsigned int n)
47{
48 return xprt->bc_alloc_count -= n;
49}
50
51/*
52 * Free the preallocated rpc_rqst structure and the memory
53 * buffers hanging off of it.
54 */
55static void xprt_free_allocation(struct rpc_rqst *req)
56{
57 struct xdr_buf *xbufp;
58
59 dprintk("RPC: free allocations for req= %p\n", req);
60 BUG_ON(test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));
61 xbufp = &req->rq_private_buf;
62 free_page((unsigned long)xbufp->head[0].iov_base);
63 xbufp = &req->rq_snd_buf;
64 free_page((unsigned long)xbufp->head[0].iov_base);
65 list_del(&req->rq_bc_pa_list);
66 kfree(req);
67}
68
69/*
70 * Preallocate up to min_reqs structures and related buffers for use
71 * by the backchannel. This function can be called multiple times
72 * when creating new sessions that use the same rpc_xprt. The
73 * preallocated buffers are added to the pool of resources used by
74 * the rpc_xprt. Anyone of these resources may be used used by an
75 * incoming callback request. It's up to the higher levels in the
76 * stack to enforce that the maximum number of session slots is not
77 * being exceeded.
78 *
79 * Some callback arguments can be large. For example, a pNFS server
80 * using multiple deviceids. The list can be unbound, but the client
81 * has the ability to tell the server the maximum size of the callback
82 * requests. Each deviceID is 16 bytes, so allocate one page
83 * for the arguments to have enough room to receive a number of these
84 * deviceIDs. The NFS client indicates to the pNFS server that its
85 * callback requests can be up to 4096 bytes in size.
86 */
87int xprt_setup_backchannel(struct rpc_xprt *xprt, unsigned int min_reqs)
88{
89 struct page *page_rcv = NULL, *page_snd = NULL;
90 struct xdr_buf *xbufp = NULL;
91 struct rpc_rqst *req, *tmp;
92 struct list_head tmp_list;
93 int i;
94
95 dprintk("RPC: setup backchannel transport\n");
96
97 /*
98 * We use a temporary list to keep track of the preallocated
99 * buffers. Once we're done building the list we splice it
100 * into the backchannel preallocation list off of the rpc_xprt
101 * struct. This helps minimize the amount of time the list
102 * lock is held on the rpc_xprt struct. It also makes cleanup
103 * easier in case of memory allocation errors.
104 */
105 INIT_LIST_HEAD(&tmp_list);
106 for (i = 0; i < min_reqs; i++) {
107 /* Pre-allocate one backchannel rpc_rqst */
108 req = kzalloc(sizeof(struct rpc_rqst), GFP_KERNEL);
109 if (req == NULL) {
110 printk(KERN_ERR "Failed to create bc rpc_rqst\n");
111 goto out_free;
112 }
113
114 /* Add the allocated buffer to the tmp list */
115 dprintk("RPC: adding req= %p\n", req);
116 list_add(&req->rq_bc_pa_list, &tmp_list);
117
118 req->rq_xprt = xprt;
119 INIT_LIST_HEAD(&req->rq_list);
120 INIT_LIST_HEAD(&req->rq_bc_list);
121
122 /* Preallocate one XDR receive buffer */
123 page_rcv = alloc_page(GFP_KERNEL);
124 if (page_rcv == NULL) {
125 printk(KERN_ERR "Failed to create bc receive xbuf\n");
126 goto out_free;
127 }
128 xbufp = &req->rq_rcv_buf;
129 xbufp->head[0].iov_base = page_address(page_rcv);
130 xbufp->head[0].iov_len = PAGE_SIZE;
131 xbufp->tail[0].iov_base = NULL;
132 xbufp->tail[0].iov_len = 0;
133 xbufp->page_len = 0;
134 xbufp->len = PAGE_SIZE;
135 xbufp->buflen = PAGE_SIZE;
136
137 /* Preallocate one XDR send buffer */
138 page_snd = alloc_page(GFP_KERNEL);
139 if (page_snd == NULL) {
140 printk(KERN_ERR "Failed to create bc snd xbuf\n");
141 goto out_free;
142 }
143
144 xbufp = &req->rq_snd_buf;
145 xbufp->head[0].iov_base = page_address(page_snd);
146 xbufp->head[0].iov_len = 0;
147 xbufp->tail[0].iov_base = NULL;
148 xbufp->tail[0].iov_len = 0;
149 xbufp->page_len = 0;
150 xbufp->len = 0;
151 xbufp->buflen = PAGE_SIZE;
152 }
153
154 /*
155 * Add the temporary list to the backchannel preallocation list
156 */
157 spin_lock_bh(&xprt->bc_pa_lock);
158 list_splice(&tmp_list, &xprt->bc_pa_list);
159 xprt_inc_alloc_count(xprt, min_reqs);
160 spin_unlock_bh(&xprt->bc_pa_lock);
161
162 dprintk("RPC: setup backchannel transport done\n");
163 return 0;
164
165out_free:
166 /*
167 * Memory allocation failed, free the temporary list
168 */
169 list_for_each_entry_safe(req, tmp, &tmp_list, rq_bc_pa_list)
170 xprt_free_allocation(req);
171
172 dprintk("RPC: setup backchannel transport failed\n");
173 return -1;
174}
175EXPORT_SYMBOL_GPL(xprt_setup_backchannel);
176
177/*
178 * Destroys the backchannel preallocated structures.
179 * Since these structures may have been allocated by multiple calls
180 * to xprt_setup_backchannel, we only destroy up to the maximum number
181 * of reqs specified by the caller.
182 * @xprt: the transport holding the preallocated strucures
183 * @max_reqs the maximum number of preallocated structures to destroy
184 */
185void xprt_destroy_backchannel(struct rpc_xprt *xprt, unsigned int max_reqs)
186{
187 struct rpc_rqst *req = NULL, *tmp = NULL;
188
189 dprintk("RPC: destroy backchannel transport\n");
190
191 BUG_ON(max_reqs == 0);
192 spin_lock_bh(&xprt->bc_pa_lock);
193 xprt_dec_alloc_count(xprt, max_reqs);
194 list_for_each_entry_safe(req, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
195 dprintk("RPC: req=%p\n", req);
196 xprt_free_allocation(req);
197 if (--max_reqs == 0)
198 break;
199 }
200 spin_unlock_bh(&xprt->bc_pa_lock);
201
202 dprintk("RPC: backchannel list empty= %s\n",
203 list_empty(&xprt->bc_pa_list) ? "true" : "false");
204}
205EXPORT_SYMBOL_GPL(xprt_destroy_backchannel);
206
207/*
208 * One or more rpc_rqst structure have been preallocated during the
209 * backchannel setup. Buffer space for the send and private XDR buffers
210 * has been preallocated as well. Use xprt_alloc_bc_request to allocate
211 * to this request. Use xprt_free_bc_request to return it.
212 *
213 * We know that we're called in soft interrupt context, grab the spin_lock
214 * since there is no need to grab the bottom half spin_lock.
215 *
216 * Return an available rpc_rqst, otherwise NULL if non are available.
217 */
218struct rpc_rqst *xprt_alloc_bc_request(struct rpc_xprt *xprt)
219{
220 struct rpc_rqst *req;
221
222 dprintk("RPC: allocate a backchannel request\n");
223 spin_lock(&xprt->bc_pa_lock);
224 if (!list_empty(&xprt->bc_pa_list)) {
225 req = list_first_entry(&xprt->bc_pa_list, struct rpc_rqst,
226 rq_bc_pa_list);
227 list_del(&req->rq_bc_pa_list);
228 } else {
229 req = NULL;
230 }
231 spin_unlock(&xprt->bc_pa_lock);
232
233 if (req != NULL) {
234 set_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
235 req->rq_reply_bytes_recvd = 0;
236 req->rq_bytes_sent = 0;
237 memcpy(&req->rq_private_buf, &req->rq_rcv_buf,
238 sizeof(req->rq_private_buf));
239 }
240 dprintk("RPC: backchannel req=%p\n", req);
241 return req;
242}
243
244/*
245 * Return the preallocated rpc_rqst structure and XDR buffers
246 * associated with this rpc_task.
247 */
248void xprt_free_bc_request(struct rpc_rqst *req)
249{
250 struct rpc_xprt *xprt = req->rq_xprt;
251
252 dprintk("RPC: free backchannel req=%p\n", req);
253
254 smp_mb__before_clear_bit();
255 BUG_ON(!test_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state));
256 clear_bit(RPC_BC_PA_IN_USE, &req->rq_bc_pa_state);
257 smp_mb__after_clear_bit();
258
259 if (!xprt_need_to_requeue(xprt)) {
260 /*
261 * The last remaining session was destroyed while this
262 * entry was in use. Free the entry and don't attempt
263 * to add back to the list because there is no need to
264 * have anymore preallocated entries.
265 */
266 dprintk("RPC: Last session removed req=%p\n", req);
267 xprt_free_allocation(req);
268 return;
269 }
270
271 /*
272 * Return it to the list of preallocations so that it
273 * may be reused by a new callback request.
274 */
275 spin_lock_bh(&xprt->bc_pa_lock);
276 list_add(&req->rq_bc_pa_list, &xprt->bc_pa_list);
277 spin_unlock_bh(&xprt->bc_pa_lock);
278}
279