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/tty.h>
9 #include <linux/tty_driver.h>
10 #include <linux/tty_flip.h>
11 #include <linux/timer.h>
12 #include <linux/string.h>
13 #include <linux/slab.h>
14 #include <linux/sched.h>
15 #include <linux/wait.h>
16 #include <linux/bitops.h>
17 #include <linux/delay.h>
18 #include <linux/module.h>
19 #include <linux/ratelimit.h>
20
21
22 #define MIN_TTYB_SIZE 256
23 #define TTYB_ALIGN_MASK 255
24
25 /*
26 * Byte threshold to limit memory consumption for flip buffers.
27 * The actual memory limit is > 2x this amount.
28 */
29 #define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
30
31 /*
32 * We default to dicing tty buffer allocations to this many characters
33 * in order to avoid multiple page allocations. We know the size of
34 * tty_buffer itself but it must also be taken into account that the
35 * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
36 * logic this must match
37 */
38
39 #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
40
41 /**
42 * tty_buffer_lock_exclusive - gain exclusive access to buffer
43 * tty_buffer_unlock_exclusive - release exclusive access
44 *
45 * @port: tty port owning the flip buffer
46 *
47 * Guarantees safe use of the line discipline's receive_buf() method by
48 * excluding the buffer work and any pending flush from using the flip
49 * buffer. Data can continue to be added concurrently to the flip buffer
50 * from the driver side.
51 *
52 * On release, the buffer work is restarted if there is data in the
53 * flip buffer
54 */
55
tty_buffer_lock_exclusive(struct tty_port * port)56 void tty_buffer_lock_exclusive(struct tty_port *port)
57 {
58 struct tty_bufhead *buf = &port->buf;
59
60 atomic_inc(&buf->priority);
61 mutex_lock(&buf->lock);
62 }
63 EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
64
tty_buffer_unlock_exclusive(struct tty_port * port)65 void tty_buffer_unlock_exclusive(struct tty_port *port)
66 {
67 struct tty_bufhead *buf = &port->buf;
68 int restart;
69
70 restart = buf->head->commit != buf->head->read;
71
72 atomic_dec(&buf->priority);
73 mutex_unlock(&buf->lock);
74 if (restart)
75 queue_work(system_unbound_wq, &buf->work);
76 }
77 EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
78
79 /**
80 * tty_buffer_space_avail - return unused buffer space
81 * @port: tty port owning the flip buffer
82 *
83 * Returns the # of bytes which can be written by the driver without
84 * reaching the buffer limit.
85 *
86 * Note: this does not guarantee that memory is available to write
87 * the returned # of bytes (use tty_prepare_flip_string_xxx() to
88 * pre-allocate if memory guarantee is required).
89 */
90
tty_buffer_space_avail(struct tty_port * port)91 int tty_buffer_space_avail(struct tty_port *port)
92 {
93 int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
94 return max(space, 0);
95 }
96 EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
97
tty_buffer_reset(struct tty_buffer * p,size_t size)98 static void tty_buffer_reset(struct tty_buffer *p, size_t size)
99 {
100 p->used = 0;
101 p->size = size;
102 p->next = NULL;
103 p->commit = 0;
104 p->read = 0;
105 p->flags = 0;
106 }
107
108 /**
109 * tty_buffer_free_all - free buffers used by a tty
110 * @port: tty port to free from
111 *
112 * Remove all the buffers pending on a tty whether queued with data
113 * or in the free ring. Must be called when the tty is no longer in use
114 */
115
tty_buffer_free_all(struct tty_port * port)116 void tty_buffer_free_all(struct tty_port *port)
117 {
118 struct tty_bufhead *buf = &port->buf;
119 struct tty_buffer *p, *next;
120 struct llist_node *llist;
121 unsigned int freed = 0;
122 int still_used;
123
124 while ((p = buf->head) != NULL) {
125 buf->head = p->next;
126 freed += p->size;
127 if (p->size > 0)
128 kfree(p);
129 }
130 llist = llist_del_all(&buf->free);
131 llist_for_each_entry_safe(p, next, llist, free)
132 kfree(p);
133
134 tty_buffer_reset(&buf->sentinel, 0);
135 buf->head = &buf->sentinel;
136 buf->tail = &buf->sentinel;
137
138 still_used = atomic_xchg(&buf->mem_used, 0);
139 WARN(still_used != freed, "we still have not freed %d bytes!",
140 still_used - freed);
141 }
142
143 /**
144 * tty_buffer_alloc - allocate a tty buffer
145 * @port: tty port
146 * @size: desired size (characters)
147 *
148 * Allocate a new tty buffer to hold the desired number of characters.
149 * We round our buffers off in 256 character chunks to get better
150 * allocation behaviour.
151 * Return NULL if out of memory or the allocation would exceed the
152 * per device queue
153 */
154
tty_buffer_alloc(struct tty_port * port,size_t size)155 static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
156 {
157 struct llist_node *free;
158 struct tty_buffer *p;
159
160 /* Round the buffer size out */
161 size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
162
163 if (size <= MIN_TTYB_SIZE) {
164 free = llist_del_first(&port->buf.free);
165 if (free) {
166 p = llist_entry(free, struct tty_buffer, free);
167 goto found;
168 }
169 }
170
171 /* Should possibly check if this fails for the largest buffer we
172 have queued and recycle that ? */
173 if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
174 return NULL;
175 p = kmalloc(sizeof(struct tty_buffer) + 2 * size,
176 GFP_ATOMIC | __GFP_NOWARN);
177 if (p == NULL)
178 return NULL;
179
180 found:
181 tty_buffer_reset(p, size);
182 atomic_add(size, &port->buf.mem_used);
183 return p;
184 }
185
186 /**
187 * tty_buffer_free - free a tty buffer
188 * @port: tty port owning the buffer
189 * @b: the buffer to free
190 *
191 * Free a tty buffer, or add it to the free list according to our
192 * internal strategy
193 */
194
tty_buffer_free(struct tty_port * port,struct tty_buffer * b)195 static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
196 {
197 struct tty_bufhead *buf = &port->buf;
198
199 /* Dumb strategy for now - should keep some stats */
200 WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
201
202 if (b->size > MIN_TTYB_SIZE)
203 kfree(b);
204 else if (b->size > 0)
205 llist_add(&b->free, &buf->free);
206 }
207
208 /**
209 * tty_buffer_flush - flush full tty buffers
210 * @tty: tty to flush
211 * @ld: optional ldisc ptr (must be referenced)
212 *
213 * flush all the buffers containing receive data. If ld != NULL,
214 * flush the ldisc input buffer.
215 *
216 * Locking: takes buffer lock to ensure single-threaded flip buffer
217 * 'consumer'
218 */
219
tty_buffer_flush(struct tty_struct * tty,struct tty_ldisc * ld)220 void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
221 {
222 struct tty_port *port = tty->port;
223 struct tty_bufhead *buf = &port->buf;
224 struct tty_buffer *next;
225
226 atomic_inc(&buf->priority);
227
228 mutex_lock(&buf->lock);
229 /* paired w/ release in __tty_buffer_request_room; ensures there are
230 * no pending memory accesses to the freed buffer
231 */
232 while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
233 tty_buffer_free(port, buf->head);
234 buf->head = next;
235 }
236 buf->head->read = buf->head->commit;
237
238 if (ld && ld->ops->flush_buffer)
239 ld->ops->flush_buffer(tty);
240
241 atomic_dec(&buf->priority);
242 mutex_unlock(&buf->lock);
243 }
244
245 /**
246 * tty_buffer_request_room - grow tty buffer if needed
247 * @port: tty port
248 * @size: size desired
249 * @flags: buffer flags if new buffer allocated (default = 0)
250 *
251 * Make at least size bytes of linear space available for the tty
252 * buffer. If we fail return the size we managed to find.
253 *
254 * Will change over to a new buffer if the current buffer is encoded as
255 * TTY_NORMAL (so has no flags buffer) and the new buffer requires
256 * a flags buffer.
257 */
__tty_buffer_request_room(struct tty_port * port,size_t size,int flags)258 static int __tty_buffer_request_room(struct tty_port *port, size_t size,
259 int flags)
260 {
261 struct tty_bufhead *buf = &port->buf;
262 struct tty_buffer *b, *n;
263 int left, change;
264
265 b = buf->tail;
266 if (b->flags & TTYB_NORMAL)
267 left = 2 * b->size - b->used;
268 else
269 left = b->size - b->used;
270
271 change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
272 if (change || left < size) {
273 /* This is the slow path - looking for new buffers to use */
274 n = tty_buffer_alloc(port, size);
275 if (n != NULL) {
276 n->flags = flags;
277 buf->tail = n;
278 /* paired w/ acquire in flush_to_ldisc(); ensures
279 * flush_to_ldisc() sees buffer data.
280 */
281 smp_store_release(&b->commit, b->used);
282 /* paired w/ acquire in flush_to_ldisc(); ensures the
283 * latest commit value can be read before the head is
284 * advanced to the next buffer
285 */
286 smp_store_release(&b->next, n);
287 } else if (change)
288 size = 0;
289 else
290 size = left;
291 }
292 return size;
293 }
294
tty_buffer_request_room(struct tty_port * port,size_t size)295 int tty_buffer_request_room(struct tty_port *port, size_t size)
296 {
297 return __tty_buffer_request_room(port, size, 0);
298 }
299 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
300
301 /**
302 * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
303 * @port: tty port
304 * @chars: characters
305 * @flag: flag value for each character
306 * @size: size
307 *
308 * Queue a series of bytes to the tty buffering. All the characters
309 * passed are marked with the supplied flag. Returns the number added.
310 */
311
tty_insert_flip_string_fixed_flag(struct tty_port * port,const unsigned char * chars,char flag,size_t size)312 int tty_insert_flip_string_fixed_flag(struct tty_port *port,
313 const unsigned char *chars, char flag, size_t size)
314 {
315 int copied = 0;
316 do {
317 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
318 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
319 int space = __tty_buffer_request_room(port, goal, flags);
320 struct tty_buffer *tb = port->buf.tail;
321 if (unlikely(space == 0))
322 break;
323 memcpy(char_buf_ptr(tb, tb->used), chars, space);
324 if (~tb->flags & TTYB_NORMAL)
325 memset(flag_buf_ptr(tb, tb->used), flag, space);
326 tb->used += space;
327 copied += space;
328 chars += space;
329 /* There is a small chance that we need to split the data over
330 several buffers. If this is the case we must loop */
331 } while (unlikely(size > copied));
332 return copied;
333 }
334 EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
335
336 /**
337 * tty_insert_flip_string_flags - Add characters to the tty buffer
338 * @port: tty port
339 * @chars: characters
340 * @flags: flag bytes
341 * @size: size
342 *
343 * Queue a series of bytes to the tty buffering. For each character
344 * the flags array indicates the status of the character. Returns the
345 * number added.
346 */
347
tty_insert_flip_string_flags(struct tty_port * port,const unsigned char * chars,const char * flags,size_t size)348 int tty_insert_flip_string_flags(struct tty_port *port,
349 const unsigned char *chars, const char *flags, size_t size)
350 {
351 int copied = 0;
352 do {
353 int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
354 int space = tty_buffer_request_room(port, goal);
355 struct tty_buffer *tb = port->buf.tail;
356 if (unlikely(space == 0))
357 break;
358 memcpy(char_buf_ptr(tb, tb->used), chars, space);
359 memcpy(flag_buf_ptr(tb, tb->used), flags, space);
360 tb->used += space;
361 copied += space;
362 chars += space;
363 flags += space;
364 /* There is a small chance that we need to split the data over
365 several buffers. If this is the case we must loop */
366 } while (unlikely(size > copied));
367 return copied;
368 }
369 EXPORT_SYMBOL(tty_insert_flip_string_flags);
370
371 /**
372 * __tty_insert_flip_char - Add one character to the tty buffer
373 * @port: tty port
374 * @ch: character
375 * @flag: flag byte
376 *
377 * Queue a single byte to the tty buffering, with an optional flag.
378 * This is the slow path of tty_insert_flip_char.
379 */
__tty_insert_flip_char(struct tty_port * port,unsigned char ch,char flag)380 int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
381 {
382 struct tty_buffer *tb;
383 int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
384
385 if (!__tty_buffer_request_room(port, 1, flags))
386 return 0;
387
388 tb = port->buf.tail;
389 if (~tb->flags & TTYB_NORMAL)
390 *flag_buf_ptr(tb, tb->used) = flag;
391 *char_buf_ptr(tb, tb->used++) = ch;
392
393 return 1;
394 }
395 EXPORT_SYMBOL(__tty_insert_flip_char);
396
397 /**
398 * tty_prepare_flip_string - make room for characters
399 * @port: tty port
400 * @chars: return pointer for character write area
401 * @size: desired size
402 *
403 * Prepare a block of space in the buffer for data. Returns the length
404 * available and buffer pointer to the space which is now allocated and
405 * accounted for as ready for normal characters. This is used for drivers
406 * that need their own block copy routines into the buffer. There is no
407 * guarantee the buffer is a DMA target!
408 */
409
tty_prepare_flip_string(struct tty_port * port,unsigned char ** chars,size_t size)410 int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
411 size_t size)
412 {
413 int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
414 if (likely(space)) {
415 struct tty_buffer *tb = port->buf.tail;
416 *chars = char_buf_ptr(tb, tb->used);
417 if (~tb->flags & TTYB_NORMAL)
418 memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
419 tb->used += space;
420 }
421 return space;
422 }
423 EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
424
425 /**
426 * tty_ldisc_receive_buf - forward data to line discipline
427 * @ld: line discipline to process input
428 * @p: char buffer
429 * @f: TTY_* flags buffer
430 * @count: number of bytes to process
431 *
432 * Callers other than flush_to_ldisc() need to exclude the kworker
433 * from concurrent use of the line discipline, see paste_selection().
434 *
435 * Returns the number of bytes processed
436 */
tty_ldisc_receive_buf(struct tty_ldisc * ld,const unsigned char * p,char * f,int count)437 int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
438 char *f, int count)
439 {
440 if (ld->ops->receive_buf2)
441 count = ld->ops->receive_buf2(ld->tty, p, f, count);
442 else {
443 count = min_t(int, count, ld->tty->receive_room);
444 if (count && ld->ops->receive_buf)
445 ld->ops->receive_buf(ld->tty, p, f, count);
446 }
447 return count;
448 }
449 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
450
451 static int
receive_buf(struct tty_port * port,struct tty_buffer * head,int count)452 receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
453 {
454 unsigned char *p = char_buf_ptr(head, head->read);
455 char *f = NULL;
456 int n;
457
458 if (~head->flags & TTYB_NORMAL)
459 f = flag_buf_ptr(head, head->read);
460
461 n = port->client_ops->receive_buf(port, p, f, count);
462 if (n > 0)
463 memset(p, 0, n);
464 return n;
465 }
466
467 /**
468 * flush_to_ldisc
469 * @work: tty structure passed from work queue.
470 *
471 * This routine is called out of the software interrupt to flush data
472 * from the buffer chain to the line discipline.
473 *
474 * The receive_buf method is single threaded for each tty instance.
475 *
476 * Locking: takes buffer lock to ensure single-threaded flip buffer
477 * 'consumer'
478 */
479
flush_to_ldisc(struct work_struct * work)480 static void flush_to_ldisc(struct work_struct *work)
481 {
482 struct tty_port *port = container_of(work, struct tty_port, buf.work);
483 struct tty_bufhead *buf = &port->buf;
484
485 mutex_lock(&buf->lock);
486
487 while (1) {
488 struct tty_buffer *head = buf->head;
489 struct tty_buffer *next;
490 int count;
491
492 /* Ldisc or user is trying to gain exclusive access */
493 if (atomic_read(&buf->priority))
494 break;
495
496 /* paired w/ release in __tty_buffer_request_room();
497 * ensures commit value read is not stale if the head
498 * is advancing to the next buffer
499 */
500 next = smp_load_acquire(&head->next);
501 /* paired w/ release in __tty_buffer_request_room() or in
502 * tty_buffer_flush(); ensures we see the committed buffer data
503 */
504 count = smp_load_acquire(&head->commit) - head->read;
505 if (!count) {
506 if (next == NULL)
507 break;
508 buf->head = next;
509 tty_buffer_free(port, head);
510 continue;
511 }
512
513 count = receive_buf(port, head, count);
514 if (!count)
515 break;
516 head->read += count;
517
518 if (need_resched())
519 cond_resched();
520 }
521
522 mutex_unlock(&buf->lock);
523
524 }
525
tty_flip_buffer_commit(struct tty_buffer * tail)526 static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
527 {
528 /*
529 * Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
530 * buffer data.
531 */
532 smp_store_release(&tail->commit, tail->used);
533 }
534
535 /**
536 * tty_flip_buffer_push - terminal
537 * @port: tty port to push
538 *
539 * Queue a push of the terminal flip buffers to the line discipline.
540 * Can be called from IRQ/atomic context.
541 *
542 * In the event of the queue being busy for flipping the work will be
543 * held off and retried later.
544 */
545
tty_flip_buffer_push(struct tty_port * port)546 void tty_flip_buffer_push(struct tty_port *port)
547 {
548 struct tty_bufhead *buf = &port->buf;
549
550 tty_flip_buffer_commit(buf->tail);
551 queue_work(system_unbound_wq, &buf->work);
552 }
553 EXPORT_SYMBOL(tty_flip_buffer_push);
554
555 /**
556 * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
557 * push
558 * @port: tty port
559 * @chars: characters
560 * @size: size
561 *
562 * The function combines tty_insert_flip_string() and tty_flip_buffer_push()
563 * with the exception of properly holding the @port->lock.
564 *
565 * To be used only internally (by pty currently).
566 *
567 * Returns: the number added.
568 */
tty_insert_flip_string_and_push_buffer(struct tty_port * port,const unsigned char * chars,size_t size)569 int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
570 const unsigned char *chars, size_t size)
571 {
572 struct tty_bufhead *buf = &port->buf;
573 unsigned long flags;
574
575 spin_lock_irqsave(&port->lock, flags);
576 size = tty_insert_flip_string(port, chars, size);
577 if (size)
578 tty_flip_buffer_commit(buf->tail);
579 spin_unlock_irqrestore(&port->lock, flags);
580
581 queue_work(system_unbound_wq, &buf->work);
582
583 return size;
584 }
585
586 /**
587 * tty_buffer_init - prepare a tty buffer structure
588 * @port: tty port to initialise
589 *
590 * Set up the initial state of the buffer management for a tty device.
591 * Must be called before the other tty buffer functions are used.
592 */
593
tty_buffer_init(struct tty_port * port)594 void tty_buffer_init(struct tty_port *port)
595 {
596 struct tty_bufhead *buf = &port->buf;
597
598 mutex_init(&buf->lock);
599 tty_buffer_reset(&buf->sentinel, 0);
600 buf->head = &buf->sentinel;
601 buf->tail = &buf->sentinel;
602 init_llist_head(&buf->free);
603 atomic_set(&buf->mem_used, 0);
604 atomic_set(&buf->priority, 0);
605 INIT_WORK(&buf->work, flush_to_ldisc);
606 buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
607 }
608
609 /**
610 * tty_buffer_set_limit - change the tty buffer memory limit
611 * @port: tty port to change
612 *
613 * Change the tty buffer memory limit.
614 * Must be called before the other tty buffer functions are used.
615 */
616
tty_buffer_set_limit(struct tty_port * port,int limit)617 int tty_buffer_set_limit(struct tty_port *port, int limit)
618 {
619 if (limit < MIN_TTYB_SIZE)
620 return -EINVAL;
621 port->buf.mem_limit = limit;
622 return 0;
623 }
624 EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
625
626 /* slave ptys can claim nested buffer lock when handling BRK and INTR */
tty_buffer_set_lock_subclass(struct tty_port * port)627 void tty_buffer_set_lock_subclass(struct tty_port *port)
628 {
629 lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
630 }
631
tty_buffer_restart_work(struct tty_port * port)632 bool tty_buffer_restart_work(struct tty_port *port)
633 {
634 return queue_work(system_unbound_wq, &port->buf.work);
635 }
636
tty_buffer_cancel_work(struct tty_port * port)637 bool tty_buffer_cancel_work(struct tty_port *port)
638 {
639 return cancel_work_sync(&port->buf.work);
640 }
641
tty_buffer_flush_work(struct tty_port * port)642 void tty_buffer_flush_work(struct tty_port *port)
643 {
644 flush_work(&port->buf.work);
645 }
646