Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0
2 : /*
3 : * Tty buffer allocation management
4 : */
5 :
6 : #include <linux/types.h>
7 : #include <linux/errno.h>
8 : #include <linux/minmax.h>
9 : #include <linux/tty.h>
10 : #include <linux/tty_buffer.h>
11 : #include <linux/tty_driver.h>
12 : #include <linux/tty_flip.h>
13 : #include <linux/timer.h>
14 : #include <linux/string.h>
15 : #include <linux/slab.h>
16 : #include <linux/sched.h>
17 : #include <linux/wait.h>
18 : #include <linux/bitops.h>
19 : #include <linux/delay.h>
20 : #include <linux/module.h>
21 : #include <linux/ratelimit.h>
22 : #include "tty.h"
23 :
24 : #define MIN_TTYB_SIZE 256
25 : #define TTYB_ALIGN_MASK 0xff
26 :
27 : /*
28 : * Byte threshold to limit memory consumption for flip buffers.
29 : * The actual memory limit is > 2x this amount.
30 : */
31 : #define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
32 :
33 : /*
34 : * We default to dicing tty buffer allocations to this many characters
35 : * in order to avoid multiple page allocations. We know the size of
36 : * tty_buffer itself but it must also be taken into account that the
37 : * buffer is 256 byte aligned. See tty_buffer_find for the allocation
38 : * logic this must match.
39 : */
40 :
41 : #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
42 :
43 : /**
44 : * tty_buffer_lock_exclusive - gain exclusive access to buffer
45 : * @port: tty port owning the flip buffer
46 : *
47 : * Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
48 : * the buffer work and any pending flush from using the flip buffer. Data can
49 : * continue to be added concurrently to the flip buffer from the driver side.
50 : *
51 : * See also tty_buffer_unlock_exclusive().
52 : */
53 0 : void tty_buffer_lock_exclusive(struct tty_port *port)
54 : {
55 0 : struct tty_bufhead *buf = &port->buf;
56 :
57 0 : atomic_inc(&buf->priority);
58 0 : mutex_lock(&buf->lock);
59 0 : }
60 : EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
61 :
62 : /**
63 : * tty_buffer_unlock_exclusive - release exclusive access
64 : * @port: tty port owning the flip buffer
65 : *
66 : * The buffer work is restarted if there is data in the flip buffer.
67 : *
68 : * See also tty_buffer_lock_exclusive().
69 : */
70 0 : void tty_buffer_unlock_exclusive(struct tty_port *port)
71 : {
72 0 : struct tty_bufhead *buf = &port->buf;
73 0 : bool restart = buf->head->commit != buf->head->read;
74 :
75 0 : atomic_dec(&buf->priority);
76 0 : mutex_unlock(&buf->lock);
77 :
78 0 : if (restart)
79 0 : queue_work(system_unbound_wq, &buf->work);
80 0 : }
81 : EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
82 :
83 : /**
84 : * tty_buffer_space_avail - return unused buffer space
85 : * @port: tty port owning the flip buffer
86 : *
87 : * Returns: the # of bytes which can be written by the driver without reaching
88 : * the buffer limit.
89 : *
90 : * Note: this does not guarantee that memory is available to write the returned
91 : * # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
92 : * guarantee is required).
93 : */
94 89 : unsigned int tty_buffer_space_avail(struct tty_port *port)
95 : {
96 89 : int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
97 :
98 89 : return max(space, 0);
99 89 : }
100 : EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
101 :
102 5 : static void tty_buffer_reset(struct tty_buffer *p, size_t size)
103 : {
104 5 : p->used = 0;
105 5 : p->size = size;
106 5 : p->next = NULL;
107 5 : p->commit = 0;
108 5 : p->lookahead = 0;
109 5 : p->read = 0;
110 5 : p->flags = true;
111 5 : }
112 :
113 : /**
114 : * tty_buffer_free_all - free buffers used by a tty
115 : * @port: tty port to free from
116 : *
117 : * Remove all the buffers pending on a tty whether queued with data or in the
118 : * free ring. Must be called when the tty is no longer in use.
119 : */
120 1 : void tty_buffer_free_all(struct tty_port *port)
121 : {
122 1 : struct tty_bufhead *buf = &port->buf;
123 1 : struct tty_buffer *p, *next;
124 1 : struct llist_node *llist;
125 1 : unsigned int freed = 0;
126 1 : int still_used;
127 :
128 2 : while ((p = buf->head) != NULL) {
129 1 : buf->head = p->next;
130 1 : freed += p->size;
131 1 : if (p->size > 0)
132 1 : kfree(p);
133 : }
134 1 : llist = llist_del_all(&buf->free);
135 1 : llist_for_each_entry_safe(p, next, llist, free)
136 0 : kfree(p);
137 :
138 1 : tty_buffer_reset(&buf->sentinel, 0);
139 1 : buf->head = &buf->sentinel;
140 1 : buf->tail = &buf->sentinel;
141 :
142 1 : still_used = atomic_xchg(&buf->mem_used, 0);
143 1 : WARN(still_used != freed, "we still have not freed %d bytes!",
144 : still_used - freed);
145 1 : }
146 :
147 : /**
148 : * tty_buffer_alloc - allocate a tty buffer
149 : * @port: tty port
150 : * @size: desired size (characters)
151 : *
152 : * Allocate a new tty buffer to hold the desired number of characters. We
153 : * round our buffers off in 256 character chunks to get better allocation
154 : * behaviour.
155 : *
156 : * Returns: %NULL if out of memory or the allocation would exceed the per
157 : * device queue.
158 : */
159 3 : static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
160 : {
161 3 : struct llist_node *free;
162 3 : struct tty_buffer *p;
163 :
164 : /* Round the buffer size out */
165 3 : size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
166 :
167 3 : if (size <= MIN_TTYB_SIZE) {
168 3 : free = llist_del_first(&port->buf.free);
169 3 : if (free) {
170 2 : p = llist_entry(free, struct tty_buffer, free);
171 2 : goto found;
172 : }
173 1 : }
174 :
175 : /* Should possibly check if this fails for the largest buffer we
176 : * have queued and recycle that ?
177 : */
178 1 : if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
179 0 : return NULL;
180 1 : p = kmalloc(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
181 1 : if (p == NULL)
182 0 : return NULL;
183 :
184 : found:
185 3 : tty_buffer_reset(p, size);
186 3 : atomic_add(size, &port->buf.mem_used);
187 3 : return p;
188 3 : }
189 :
190 : /**
191 : * tty_buffer_free - free a tty buffer
192 : * @port: tty port owning the buffer
193 : * @b: the buffer to free
194 : *
195 : * Free a tty buffer, or add it to the free list according to our internal
196 : * strategy.
197 : */
198 3 : static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
199 : {
200 3 : struct tty_bufhead *buf = &port->buf;
201 :
202 : /* Dumb strategy for now - should keep some stats */
203 3 : WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
204 :
205 3 : if (b->size > MIN_TTYB_SIZE)
206 0 : kfree(b);
207 3 : else if (b->size > 0)
208 2 : llist_add(&b->free, &buf->free);
209 3 : }
210 :
211 : /**
212 : * tty_buffer_flush - flush full tty buffers
213 : * @tty: tty to flush
214 : * @ld: optional ldisc ptr (must be referenced)
215 : *
216 : * Flush all the buffers containing receive data. If @ld != %NULL, flush the
217 : * ldisc input buffer.
218 : *
219 : * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
220 : */
221 12 : void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
222 : {
223 12 : struct tty_port *port = tty->port;
224 12 : struct tty_bufhead *buf = &port->buf;
225 12 : struct tty_buffer *next;
226 :
227 12 : atomic_inc(&buf->priority);
228 :
229 12 : mutex_lock(&buf->lock);
230 : /* paired w/ release in __tty_buffer_request_room; ensures there are
231 : * no pending memory accesses to the freed buffer
232 : */
233 12 : while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
234 0 : tty_buffer_free(port, buf->head);
235 0 : buf->head = next;
236 : }
237 12 : buf->head->read = buf->head->commit;
238 12 : buf->head->lookahead = buf->head->read;
239 :
240 12 : if (ld && ld->ops->flush_buffer)
241 12 : ld->ops->flush_buffer(tty);
242 :
243 12 : atomic_dec(&buf->priority);
244 12 : mutex_unlock(&buf->lock);
245 12 : }
246 :
247 : /**
248 : * __tty_buffer_request_room - grow tty buffer if needed
249 : * @port: tty port
250 : * @size: size desired
251 : * @flags: buffer has to store flags along character data
252 : *
253 : * Make at least @size bytes of linear space available for the tty buffer.
254 : *
255 : * Will change over to a new buffer if the current buffer is encoded as
256 : * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
257 : * buffer.
258 : *
259 : * Returns: the size we managed to find.
260 : */
261 53 : static int __tty_buffer_request_room(struct tty_port *port, size_t size,
262 : bool flags)
263 : {
264 53 : struct tty_bufhead *buf = &port->buf;
265 53 : struct tty_buffer *n, *b = buf->tail;
266 53 : size_t left = (b->flags ? 1 : 2) * b->size - b->used;
267 53 : bool change = !b->flags && flags;
268 :
269 53 : if (!change && left >= size)
270 50 : return size;
271 :
272 : /* This is the slow path - looking for new buffers to use */
273 3 : n = tty_buffer_alloc(port, size);
274 3 : if (n == NULL)
275 0 : return change ? 0 : left;
276 :
277 3 : n->flags = flags;
278 3 : buf->tail = n;
279 : /*
280 : * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
281 : * ensures they see all buffer data.
282 : */
283 3 : smp_store_release(&b->commit, b->used);
284 : /*
285 : * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
286 : * ensures the latest commit value can be read before the head
287 : * is advanced to the next buffer.
288 : */
289 3 : smp_store_release(&b->next, n);
290 :
291 3 : return size;
292 53 : }
293 :
294 0 : int tty_buffer_request_room(struct tty_port *port, size_t size)
295 : {
296 0 : return __tty_buffer_request_room(port, size, true);
297 : }
298 : EXPORT_SYMBOL_GPL(tty_buffer_request_room);
299 :
300 53 : size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
301 : const u8 *flags, bool mutable_flags,
302 : size_t size)
303 : {
304 53 : bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
305 53 : size_t copied = 0;
306 :
307 53 : do {
308 53 : size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
309 53 : size_t space = __tty_buffer_request_room(port, goal, need_flags);
310 53 : struct tty_buffer *tb = port->buf.tail;
311 :
312 53 : if (unlikely(space == 0))
313 0 : break;
314 :
315 53 : memcpy(char_buf_ptr(tb, tb->used), chars, space);
316 :
317 53 : if (mutable_flags) {
318 0 : memcpy(flag_buf_ptr(tb, tb->used), flags, space);
319 0 : flags += space;
320 53 : } else if (tb->flags) {
321 0 : memset(flag_buf_ptr(tb, tb->used), flags[0], space);
322 0 : } else {
323 : /* tb->flags should be available once requested */
324 53 : WARN_ON_ONCE(need_flags);
325 : }
326 :
327 53 : tb->used += space;
328 53 : copied += space;
329 53 : chars += space;
330 :
331 : /* There is a small chance that we need to split the data over
332 : * several buffers. If this is the case we must loop.
333 : */
334 53 : } while (unlikely(size > copied));
335 :
336 106 : return copied;
337 53 : }
338 : EXPORT_SYMBOL(__tty_insert_flip_string_flags);
339 :
340 : /**
341 : * tty_prepare_flip_string - make room for characters
342 : * @port: tty port
343 : * @chars: return pointer for character write area
344 : * @size: desired size
345 : *
346 : * Prepare a block of space in the buffer for data.
347 : *
348 : * This is used for drivers that need their own block copy routines into the
349 : * buffer. There is no guarantee the buffer is a DMA target!
350 : *
351 : * Returns: the length available and buffer pointer (@chars) to the space which
352 : * is now allocated and accounted for as ready for normal characters.
353 : */
354 0 : size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
355 : {
356 0 : size_t space = __tty_buffer_request_room(port, size, false);
357 :
358 0 : if (likely(space)) {
359 0 : struct tty_buffer *tb = port->buf.tail;
360 :
361 0 : *chars = char_buf_ptr(tb, tb->used);
362 0 : if (tb->flags)
363 0 : memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
364 0 : tb->used += space;
365 0 : }
366 :
367 0 : return space;
368 0 : }
369 : EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
370 :
371 : /**
372 : * tty_ldisc_receive_buf - forward data to line discipline
373 : * @ld: line discipline to process input
374 : * @p: char buffer
375 : * @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
376 : * @count: number of bytes to process
377 : *
378 : * Callers other than flush_to_ldisc() need to exclude the kworker from
379 : * concurrent use of the line discipline, see paste_selection().
380 : *
381 : * Returns: the number of bytes processed.
382 : */
383 21 : size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
384 : size_t count)
385 : {
386 21 : if (ld->ops->receive_buf2)
387 21 : count = ld->ops->receive_buf2(ld->tty, p, f, count);
388 : else {
389 0 : count = min_t(size_t, count, ld->tty->receive_room);
390 0 : if (count && ld->ops->receive_buf)
391 0 : ld->ops->receive_buf(ld->tty, p, f, count);
392 : }
393 21 : return count;
394 : }
395 : EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
396 :
397 0 : static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
398 : {
399 0 : head->lookahead = max(head->lookahead, head->read);
400 :
401 0 : while (head) {
402 0 : struct tty_buffer *next;
403 0 : unsigned int count;
404 :
405 : /*
406 : * Paired w/ release in __tty_buffer_request_room();
407 : * ensures commit value read is not stale if the head
408 : * is advancing to the next buffer.
409 : */
410 0 : next = smp_load_acquire(&head->next);
411 : /*
412 : * Paired w/ release in __tty_buffer_request_room() or in
413 : * tty_buffer_flush(); ensures we see the committed buffer data.
414 : */
415 0 : count = smp_load_acquire(&head->commit) - head->lookahead;
416 0 : if (!count) {
417 0 : head = next;
418 0 : continue;
419 : }
420 :
421 0 : if (port->client_ops->lookahead_buf) {
422 0 : u8 *p, *f = NULL;
423 :
424 0 : p = char_buf_ptr(head, head->lookahead);
425 0 : if (head->flags)
426 0 : f = flag_buf_ptr(head, head->lookahead);
427 :
428 0 : port->client_ops->lookahead_buf(port, p, f, count);
429 0 : }
430 :
431 0 : head->lookahead += count;
432 0 : }
433 0 : }
434 :
435 : static size_t
436 21 : receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
437 : {
438 21 : u8 *p = char_buf_ptr(head, head->read);
439 21 : const u8 *f = NULL;
440 21 : size_t n;
441 :
442 21 : if (head->flags)
443 0 : f = flag_buf_ptr(head, head->read);
444 :
445 21 : n = port->client_ops->receive_buf(port, p, f, count);
446 21 : if (n > 0)
447 21 : memset(p, 0, n);
448 42 : return n;
449 21 : }
450 :
451 : /**
452 : * flush_to_ldisc - flush data from buffer to ldisc
453 : * @work: tty structure passed from work queue.
454 : *
455 : * This routine is called out of the software interrupt to flush data from the
456 : * buffer chain to the line discipline.
457 : *
458 : * The receive_buf() method is single threaded for each tty instance.
459 : *
460 : * Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
461 : */
462 19 : static void flush_to_ldisc(struct work_struct *work)
463 : {
464 19 : struct tty_port *port = container_of(work, struct tty_port, buf.work);
465 19 : struct tty_bufhead *buf = &port->buf;
466 :
467 19 : mutex_lock(&buf->lock);
468 :
469 43 : while (1) {
470 43 : struct tty_buffer *head = buf->head;
471 43 : struct tty_buffer *next;
472 43 : size_t count, rcvd;
473 :
474 : /* Ldisc or user is trying to gain exclusive access */
475 43 : if (atomic_read(&buf->priority))
476 0 : break;
477 :
478 : /* paired w/ release in __tty_buffer_request_room();
479 : * ensures commit value read is not stale if the head
480 : * is advancing to the next buffer
481 : */
482 43 : next = smp_load_acquire(&head->next);
483 : /* paired w/ release in __tty_buffer_request_room() or in
484 : * tty_buffer_flush(); ensures we see the committed buffer data
485 : */
486 43 : count = smp_load_acquire(&head->commit) - head->read;
487 43 : if (!count) {
488 22 : if (next == NULL)
489 19 : break;
490 3 : buf->head = next;
491 3 : tty_buffer_free(port, head);
492 3 : continue;
493 : }
494 :
495 21 : rcvd = receive_buf(port, head, count);
496 21 : head->read += rcvd;
497 21 : if (rcvd < count)
498 0 : lookahead_bufs(port, head);
499 21 : if (!rcvd)
500 0 : break;
501 :
502 21 : cond_resched();
503 43 : }
504 :
505 19 : mutex_unlock(&buf->lock);
506 :
507 19 : }
508 :
509 53 : static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
510 : {
511 : /*
512 : * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
513 : * buffer data.
514 : */
515 53 : smp_store_release(&tail->commit, tail->used);
516 53 : }
517 :
518 : /**
519 : * tty_flip_buffer_push - push terminal buffers
520 : * @port: tty port to push
521 : *
522 : * Queue a push of the terminal flip buffers to the line discipline. Can be
523 : * called from IRQ/atomic context.
524 : *
525 : * In the event of the queue being busy for flipping the work will be held off
526 : * and retried later.
527 : */
528 1 : void tty_flip_buffer_push(struct tty_port *port)
529 : {
530 1 : struct tty_bufhead *buf = &port->buf;
531 :
532 1 : tty_flip_buffer_commit(buf->tail);
533 1 : queue_work(system_unbound_wq, &buf->work);
534 1 : }
535 : EXPORT_SYMBOL(tty_flip_buffer_push);
536 :
537 : /**
538 : * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
539 : * push
540 : * @port: tty port
541 : * @chars: characters
542 : * @size: size
543 : *
544 : * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
545 : * with the exception of properly holding the @port->lock.
546 : *
547 : * To be used only internally (by pty currently).
548 : *
549 : * Returns: the number added.
550 : */
551 52 : int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
552 : const u8 *chars, size_t size)
553 : {
554 52 : struct tty_bufhead *buf = &port->buf;
555 52 : unsigned long flags;
556 :
557 52 : spin_lock_irqsave(&port->lock, flags);
558 52 : size = tty_insert_flip_string(port, chars, size);
559 52 : if (size)
560 52 : tty_flip_buffer_commit(buf->tail);
561 52 : spin_unlock_irqrestore(&port->lock, flags);
562 :
563 52 : queue_work(system_unbound_wq, &buf->work);
564 :
565 104 : return size;
566 52 : }
567 :
568 : /**
569 : * tty_buffer_init - prepare a tty buffer structure
570 : * @port: tty port to initialise
571 : *
572 : * Set up the initial state of the buffer management for a tty device. Must be
573 : * called before the other tty buffer functions are used.
574 : */
575 1 : void tty_buffer_init(struct tty_port *port)
576 : {
577 1 : struct tty_bufhead *buf = &port->buf;
578 :
579 1 : mutex_init(&buf->lock);
580 1 : tty_buffer_reset(&buf->sentinel, 0);
581 1 : buf->head = &buf->sentinel;
582 1 : buf->tail = &buf->sentinel;
583 1 : init_llist_head(&buf->free);
584 1 : atomic_set(&buf->mem_used, 0);
585 1 : atomic_set(&buf->priority, 0);
586 1 : INIT_WORK(&buf->work, flush_to_ldisc);
587 1 : buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
588 1 : }
589 :
590 : /**
591 : * tty_buffer_set_limit - change the tty buffer memory limit
592 : * @port: tty port to change
593 : * @limit: memory limit to set
594 : *
595 : * Change the tty buffer memory limit.
596 : *
597 : * Must be called before the other tty buffer functions are used.
598 : */
599 0 : int tty_buffer_set_limit(struct tty_port *port, int limit)
600 : {
601 0 : if (limit < MIN_TTYB_SIZE)
602 0 : return -EINVAL;
603 0 : port->buf.mem_limit = limit;
604 0 : return 0;
605 0 : }
606 : EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
607 :
608 : /* slave ptys can claim nested buffer lock when handling BRK and INTR */
609 0 : void tty_buffer_set_lock_subclass(struct tty_port *port)
610 : {
611 0 : lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
612 0 : }
613 :
614 0 : bool tty_buffer_restart_work(struct tty_port *port)
615 : {
616 0 : return queue_work(system_unbound_wq, &port->buf.work);
617 : }
618 :
619 7 : bool tty_buffer_cancel_work(struct tty_port *port)
620 : {
621 7 : return cancel_work_sync(&port->buf.work);
622 : }
623 :
624 74 : void tty_buffer_flush_work(struct tty_port *port)
625 : {
626 74 : flush_work(&port->buf.work);
627 74 : }
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