// SPDX-License-Identifier: GPL-2.0
/*
* Tty buffer allocation management
*/
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/minmax.h>
#include <linux/tty.h>
#include <linux/tty_buffer.h>
#include <linux/tty_driver.h>
#include <linux/tty_flip.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/wait.h>
#include <linux/bitops.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/ratelimit.h>
#include "tty.h"
#define MIN_TTYB_SIZE 256
#define TTYB_ALIGN_MASK 0xff
/*
* Byte threshold to limit memory consumption for flip buffers.
* The actual memory limit is > 2x this amount.
*/
#define TTYB_DEFAULT_MEM_LIMIT (640 * 1024UL)
/*
* We default to dicing tty buffer allocations to this many characters
* in order to avoid multiple page allocations. We know the size of
* tty_buffer itself but it must also be taken into account that the
* buffer is 256 byte aligned. See tty_buffer_find for the allocation
* logic this must match.
*/
#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
/**
* tty_buffer_lock_exclusive - gain exclusive access to buffer
* @port: tty port owning the flip buffer
*
* Guarantees safe use of the &tty_ldisc_ops.receive_buf() method by excluding
* the buffer work and any pending flush from using the flip buffer. Data can
* continue to be added concurrently to the flip buffer from the driver side.
*
* See also tty_buffer_unlock_exclusive().
*/
void tty_buffer_lock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
}
EXPORT_SYMBOL_GPL(tty_buffer_lock_exclusive);
/**
* tty_buffer_unlock_exclusive - release exclusive access
* @port: tty port owning the flip buffer
*
* The buffer work is restarted if there is data in the flip buffer.
*
* See also tty_buffer_lock_exclusive().
*/
void tty_buffer_unlock_exclusive(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
bool restart = buf->head->commit != buf->head->read;
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
if (restart)
queue_work(system_unbound_wq, &buf->work);
}
EXPORT_SYMBOL_GPL(tty_buffer_unlock_exclusive);
/**
* tty_buffer_space_avail - return unused buffer space
* @port: tty port owning the flip buffer
*
* Returns: the # of bytes which can be written by the driver without reaching
* the buffer limit.
*
* Note: this does not guarantee that memory is available to write the returned
* # of bytes (use tty_prepare_flip_string() to pre-allocate if memory
* guarantee is required).
*/
unsigned int tty_buffer_space_avail(struct tty_port *port)
{
int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used);
return max(space, 0);
}
EXPORT_SYMBOL_GPL(tty_buffer_space_avail);
static void tty_buffer_reset(struct tty_buffer *p, size_t size)
{
p->used = 0;
p->size = size;
p->next = NULL;
p->commit = 0;
p->lookahead = 0;
p->read = 0;
p->flags = true;
}
/**
* tty_buffer_free_all - free buffers used by a tty
* @port: tty port to free from
*
* Remove all the buffers pending on a tty whether queued with data or in the
* free ring. Must be called when the tty is no longer in use.
*/
void tty_buffer_free_all(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *p, *next;
struct llist_node *llist;
unsigned int freed = 0;
int still_used;
while ((p = buf->head) != NULL) {
buf->head = p->next;
freed += p->size;
if (p->size > 0)
kfree(p);
}
llist = llist_del_all(&buf->free);
llist_for_each_entry_safe(p, next, llist, free)
kfree(p);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
still_used = atomic_xchg(&buf->mem_used, 0);
WARN(still_used != freed, "we still have not freed %d bytes!",
still_used - freed);
}
/**
* tty_buffer_alloc - allocate a tty buffer
* @port: tty port
* @size: desired size (characters)
*
* Allocate a new tty buffer to hold the desired number of characters. We
* round our buffers off in 256 character chunks to get better allocation
* behaviour.
*
* Returns: %NULL if out of memory or the allocation would exceed the per
* device queue.
*/
static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
{
struct llist_node *free;
struct tty_buffer *p;
/* Round the buffer size out */
size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
if (size <= MIN_TTYB_SIZE) {
free = llist_del_first(&port->buf.free);
if (free) {
p = llist_entry(free, struct tty_buffer, free);
goto found;
}
}
/* Should possibly check if this fails for the largest buffer we
* have queued and recycle that ?
*/
if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
return NULL;
p = kmalloc(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
if (p == NULL)
return NULL;
found:
tty_buffer_reset(p, size);
atomic_add(size, &port->buf.mem_used);
return p;
}
/**
* tty_buffer_free - free a tty buffer
* @port: tty port owning the buffer
* @b: the buffer to free
*
* Free a tty buffer, or add it to the free list according to our internal
* strategy.
*/
static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
{
struct tty_bufhead *buf = &port->buf;
/* Dumb strategy for now - should keep some stats */
WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0);
if (b->size > MIN_TTYB_SIZE)
kfree(b);
else if (b->size > 0)
llist_add(&b->free, &buf->free);
}
/**
* tty_buffer_flush - flush full tty buffers
* @tty: tty to flush
* @ld: optional ldisc ptr (must be referenced)
*
* Flush all the buffers containing receive data. If @ld != %NULL, flush the
* ldisc input buffer.
*
* Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
*/
void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
{
struct tty_port *port = tty->port;
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *next;
atomic_inc(&buf->priority);
mutex_lock(&buf->lock);
/* paired w/ release in __tty_buffer_request_room; ensures there are
* no pending memory accesses to the freed buffer
*/
while ((next = smp_load_acquire(&buf->head->next)) != NULL) {
tty_buffer_free(port, buf->head);
buf->head = next;
}
buf->head->read = buf->head->commit;
buf->head->lookahead = buf->head->read;
if (ld && ld->ops->flush_buffer)
ld->ops->flush_buffer(tty);
atomic_dec(&buf->priority);
mutex_unlock(&buf->lock);
}
/**
* __tty_buffer_request_room - grow tty buffer if needed
* @port: tty port
* @size: size desired
* @flags: buffer has to store flags along character data
*
* Make at least @size bytes of linear space available for the tty buffer.
*
* Will change over to a new buffer if the current buffer is encoded as
* %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
* buffer.
*
* Returns: the size we managed to find.
*/
static int __tty_buffer_request_room(struct tty_port *port, size_t size,
bool flags)
{
struct tty_bufhead *buf = &port->buf;
struct tty_buffer *n, *b = buf->tail;
size_t left = (b->flags ? 1 : 2) * b->size - b->used;
bool change = !b->flags && flags;
if (!change && left >= size)
return size;
/* This is the slow path - looking for new buffers to use */
n = tty_buffer_alloc(port, size);
if (n == NULL)
return change ? 0 : left;
n->flags = flags;
buf->tail = n;
/*
* Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
* ensures they see all buffer data.
*/
smp_store_release(&b->commit, b->used);
/*
* Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
* ensures the latest commit value can be read before the head
* is advanced to the next buffer.
*/
smp_store_release(&b->next, n);
return size;
}
int tty_buffer_request_room(struct tty_port *port, size_t size)
{
return __tty_buffer_request_room(port, size, true);
}
EXPORT_SYMBOL_GPL(tty_buffer_request_room);
size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
const u8 *flags, bool mutable_flags,
size_t size)
{
bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
size_t copied = 0;
do {
size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
size_t space = __tty_buffer_request_room(port, goal, need_flags);
struct tty_buffer *tb = port->buf.tail;
if (unlikely(space == 0))
break;
memcpy(char_buf_ptr(tb, tb->used), chars, space);
if (mutable_flags) {
memcpy(flag_buf_ptr(tb, tb->used), flags, space);
flags += space;
} else if (tb->flags) {
memset(flag_buf_ptr(tb, tb->used), flags[0], space);
} else {
/* tb->flags should be available once requested */
WARN_ON_ONCE(need_flags);
}
tb->used += space;
copied += space;
chars += space;
/* There is a small chance that we need to split the data over
* several buffers. If this is the case we must loop.
*/
} while (unlikely(size > copied));
return copied;
}
EXPORT_SYMBOL(__tty_insert_flip_string_flags);
/**
* tty_prepare_flip_string - make room for characters
* @port: tty port
* @chars: return pointer for character write area
* @size: desired size
*
* Prepare a block of space in the buffer for data.
*
* This is used for drivers that need their own block copy routines into the
* buffer. There is no guarantee the buffer is a DMA target!
*
* Returns: the length available and buffer pointer (@chars) to the space which
* is now allocated and accounted for as ready for normal characters.
*/
size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
{
size_t space = __tty_buffer_request_room(port, size, false);
if (likely(space)) {
struct tty_buffer *tb = port->buf.tail;
*chars = char_buf_ptr(tb, tb->used);
if (tb->flags)
memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space);
tb->used += space;
}
return space;
}
EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
/**
* tty_ldisc_receive_buf - forward data to line discipline
* @ld: line discipline to process input
* @p: char buffer
* @f: %TTY_NORMAL, %TTY_BREAK, etc. flags buffer
* @count: number of bytes to process
*
* Callers other than flush_to_ldisc() need to exclude the kworker from
* concurrent use of the line discipline, see paste_selection().
*
* Returns: the number of bytes processed.
*/
size_t tty_ldisc_receive_buf(struct tty_ldisc *ld, const u8 *p, const u8 *f,
size_t count)
{
if (ld->ops->receive_buf2)
count = ld->ops->receive_buf2(ld->tty, p, f, count);
else {
count = min_t(size_t, count, ld->tty->receive_room);
if (count && ld->ops->receive_buf)
ld->ops->receive_buf(ld->tty, p, f, count);
}
return count;
}
EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
static void lookahead_bufs(struct tty_port *port, struct tty_buffer *head)
{
head->lookahead = max(head->lookahead, head->read);
while (head) {
struct tty_buffer *next;
unsigned int count;
/*
* Paired w/ release in __tty_buffer_request_room();
* ensures commit value read is not stale if the head
* is advancing to the next buffer.
*/
next = smp_load_acquire(&head->next);
/*
* Paired w/ release in __tty_buffer_request_room() or in
* tty_buffer_flush(); ensures we see the committed buffer data.
*/
count = smp_load_acquire(&head->commit) - head->lookahead;
if (!count) {
head = next;
continue;
}
if (port->client_ops->lookahead_buf) {
u8 *p, *f = NULL;
p = char_buf_ptr(head, head->lookahead);
if (head->flags)
f = flag_buf_ptr(head, head->lookahead);
port->client_ops->lookahead_buf(port, p, f, count);
}
head->lookahead += count;
}
}
static size_t
receive_buf(struct tty_port *port, struct tty_buffer *head, size_t count)
{
u8 *p = char_buf_ptr(head, head->read);
const u8 *f = NULL;
size_t n;
if (head->flags)
f = flag_buf_ptr(head, head->read);
n = port->client_ops->receive_buf(port, p, f, count);
if (n > 0)
memset(p, 0, n);
return n;
}
/**
* flush_to_ldisc - flush data from buffer to ldisc
* @work: tty structure passed from work queue.
*
* This routine is called out of the software interrupt to flush data from the
* buffer chain to the line discipline.
*
* The receive_buf() method is single threaded for each tty instance.
*
* Locking: takes buffer lock to ensure single-threaded flip buffer 'consumer'.
*/
static void flush_to_ldisc(struct work_struct *work)
{
struct tty_port *port = container_of(work, struct tty_port, buf.work);
struct tty_bufhead *buf = &port->buf;
mutex_lock(&buf->lock);
while (1) {
struct tty_buffer *head = buf->head;
struct tty_buffer *next;
size_t count, rcvd;
/* Ldisc or user is trying to gain exclusive access */
if (atomic_read(&buf->priority))
break;
/* paired w/ release in __tty_buffer_request_room();
* ensures commit value read is not stale if the head
* is advancing to the next buffer
*/
next = smp_load_acquire(&head->next);
/* paired w/ release in __tty_buffer_request_room() or in
* tty_buffer_flush(); ensures we see the committed buffer data
*/
count = smp_load_acquire(&head->commit) - head->read;
if (!count) {
if (next == NULL)
break;
buf->head = next;
tty_buffer_free(port, head);
continue;
}
rcvd = receive_buf(port, head, count);
head->read += rcvd;
if (rcvd < count)
lookahead_bufs(port, head);
if (!rcvd)
break;
if (need_resched())
cond_resched();
}
mutex_unlock(&buf->lock);
}
static inline void tty_flip_buffer_commit(struct tty_buffer *tail)
{
/*
* Paired w/ acquire in flush_to_ldisc(); ensures flush_to_ldisc() sees
* buffer data.
*/
smp_store_release(&tail->commit, tail->used);
}
/**
* tty_flip_buffer_push - push terminal buffers
* @port: tty port to push
*
* Queue a push of the terminal flip buffers to the line discipline. Can be
* called from IRQ/atomic context.
*
* In the event of the queue being busy for flipping the work will be held off
* and retried later.
*/
void tty_flip_buffer_push(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
tty_flip_buffer_commit(buf->tail);
queue_work(system_unbound_wq, &buf->work);
}
EXPORT_SYMBOL(tty_flip_buffer_push);
/**
* tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
* push
* @port: tty port
* @chars: characters
* @size: size
*
* The function combines tty_insert_flip_string() and tty_flip_buffer_push()
* with the exception of properly holding the @port->lock.
*
* To be used only internally (by pty currently).
*
* Returns: the number added.
*/
int tty_insert_flip_string_and_push_buffer(struct tty_port *port,
const u8 *chars, size_t size)
{
struct tty_bufhead *buf = &port->buf;
unsigned long flags;
spin_lock_irqsave(&port->lock, flags);
size = tty_insert_flip_string(port, chars, size);
if (size)
tty_flip_buffer_commit(buf->tail);
spin_unlock_irqrestore(&port->lock, flags);
queue_work(system_unbound_wq, &buf->work);
return size;
}
/**
* tty_buffer_init - prepare a tty buffer structure
* @port: tty port to initialise
*
* Set up the initial state of the buffer management for a tty device. Must be
* called before the other tty buffer functions are used.
*/
void tty_buffer_init(struct tty_port *port)
{
struct tty_bufhead *buf = &port->buf;
mutex_init(&buf->lock);
tty_buffer_reset(&buf->sentinel, 0);
buf->head = &buf->sentinel;
buf->tail = &buf->sentinel;
init_llist_head(&buf->free);
atomic_set(&buf->mem_used, 0);
atomic_set(&buf->priority, 0);
INIT_WORK(&buf->work, flush_to_ldisc);
buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
}
/**
* tty_buffer_set_limit - change the tty buffer memory limit
* @port: tty port to change
* @limit: memory limit to set
*
* Change the tty buffer memory limit.
*
* Must be called before the other tty buffer functions are used.
*/
int tty_buffer_set_limit(struct tty_port *port, int limit)
{
if (limit < MIN_TTYB_SIZE)
return -EINVAL;
port->buf.mem_limit = limit;
return 0;
}
EXPORT_SYMBOL_GPL(tty_buffer_set_limit);
/* slave ptys can claim nested buffer lock when handling BRK and INTR */
void tty_buffer_set_lock_subclass(struct tty_port *port)
{
lockdep_set_subclass(&port->buf.lock, TTY_LOCK_SLAVE);
}
bool tty_buffer_restart_work(struct tty_port *port)
{
return queue_work(system_unbound_wq, &port->buf.work);
}
bool tty_buffer_cancel_work(struct tty_port *port)
{
return cancel_work_sync(&port->buf.work);
}
void tty_buffer_flush_work(struct tty_port *port)
{
flush_work(&port->buf.work);
}
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