1 files changed, 270 insertions, 262 deletions

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 77070c2d1240..1a5673acd9b1 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -5,7 +5,9 @@
 
 #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>
@@ -17,42 +19,37 @@
 #include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/ratelimit.h>
-
+#include "tty.h"
 
 #define MIN_TTYB_SIZE	256
-#define TTYB_ALIGN_MASK	255
+#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	65536
+#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
- * the buffer is 256 byte aligned. See tty_buffer_find for the allocation
- * logic this must match
+ * 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) & ~0xFF)
+#define TTY_BUFFER_PAGE	(((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~TTYB_ALIGN_MASK)
 
 /**
- *	tty_buffer_lock_exclusive	-	gain exclusive access to buffer
- *	tty_buffer_unlock_exclusive	-	release exclusive access
- *
- *	@port - tty_port owning the flip buffer
+ * tty_buffer_lock_exclusive	-	gain exclusive access to buffer
+ * @port: tty port owning the flip buffer
  *
- *	Guarantees safe use of the line discipline's 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.
+ * 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.
  *
- *	On release, the buffer work is restarted if there is data in the
- *	flip buffer
+ * See also tty_buffer_unlock_exclusive().
  */
-
 void tty_buffer_lock_exclusive(struct tty_port *port)
 {
 	struct tty_bufhead *buf = &port->buf;
@@ -62,35 +59,42 @@ void tty_buffer_lock_exclusive(struct tty_port *port)
 }
 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;
-	int restart;
-
-	restart = buf->head->commit != buf->head->read;
+	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);
+		queue_work(system_dfl_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
+ * 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.
+ * 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_xxx() to
- *	pre-allocate if memory guarantee is required).
+ * 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).
  */
-
-int tty_buffer_space_avail(struct tty_port *port)
+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);
@@ -101,18 +105,18 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size)
 	p->size = size;
 	p->next = NULL;
 	p->commit = 0;
+	p->lookahead = 0;
 	p->read = 0;
-	p->flags = 0;
+	p->flags = true;
 }
 
 /**
- *	tty_buffer_free_all		-	free buffers used by a tty
- *	@tty: tty to free from
+ * 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
+ * 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;
@@ -141,17 +145,17 @@ void tty_buffer_free_all(struct tty_port *port)
 }
 
 /**
- *	tty_buffer_alloc	-	allocate a tty buffer
- *	@tty: tty device
- *	@size: desired size (characters)
+ * 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.
  *
- *	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.
- *	Return NULL if out of memory or the allocation would exceed the
- *	per device queue
+ * 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;
@@ -169,10 +173,11 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
 	}
 
 	/* Should possibly check if this fails for the largest buffer we
-	   have queued and recycle that ? */
+	 * have queued and recycle that ?
+	 */
 	if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
 		return NULL;
-	p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
+	p = kmalloc(struct_size(p, data, 2 * size), GFP_ATOMIC | __GFP_NOWARN);
 	if (p == NULL)
 		return NULL;
 
@@ -183,14 +188,13 @@ found:
 }
 
 /**
- *	tty_buffer_free		-	free a tty buffer
- *	@tty: tty owning the buffer
- *	@b: the buffer to free
+ * 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
+ * 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;
@@ -205,17 +209,15 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
 }
 
 /**
- *	tty_buffer_flush		-	flush full tty buffers
- *	@tty: tty to flush
- *	@ld:  optional ldisc ptr (must be referenced)
+ * 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.
+ * 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'
+ * 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;
@@ -233,6 +235,7 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
 		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);
@@ -242,225 +245,148 @@ void tty_buffer_flush(struct tty_struct *tty, struct tty_ldisc *ld)
 }
 
 /**
- *	tty_buffer_request_room		-	grow tty buffer if needed
- *	@tty: tty structure
- *	@size: size desired
- *	@flags: buffer flags if new buffer allocated (default = 0)
+ * __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.
  *
- *	Make at least size bytes of linear space available for the tty
- *	buffer. If we fail return the size we managed to find.
+ * 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.
  *
- *	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,
-				     int flags)
+				     bool flags)
 {
 	struct tty_bufhead *buf = &port->buf;
-	struct tty_buffer *b, *n;
-	int left, change;
-
-	b = buf->tail;
-	if (b->flags & TTYB_NORMAL)
-		left = 2 * b->size - b->used;
-	else
-		left = b->size - b->used;
-
-	change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
-	if (change || left < size) {
-		/* This is the slow path - looking for new buffers to use */
-		n = tty_buffer_alloc(port, size);
-		if (n != NULL) {
-			n->flags = flags;
-			buf->tail = n;
-			/* paired w/ acquire in flush_to_ldisc(); ensures
-			 * flush_to_ldisc() sees buffer data.
-			 */
-			smp_store_release(&b->commit, b->used);
-			/* paired w/ acquire in flush_to_ldisc(); ensures the
-			 * latest commit value can be read before the head is
-			 * advanced to the next buffer
-			 */
-			smp_store_release(&b->next, n);
-		} else if (change)
-			size = 0;
-		else
-			size = left;
-	}
+	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, 0);
+	return __tty_buffer_request_room(port, size, true);
 }
 EXPORT_SYMBOL_GPL(tty_buffer_request_room);
 
-/**
- *	tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
- *	@port: tty port
- *	@chars: characters
- *	@flag: flag value for each character
- *	@size: size
- *
- *	Queue a series of bytes to the tty buffering. All the characters
- *	passed are marked with the supplied flag. Returns the number added.
- */
-
-int tty_insert_flip_string_fixed_flag(struct tty_port *port,
-		const unsigned char *chars, char flag, size_t size)
+size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
+				      const u8 *flags, bool mutable_flags,
+				      size_t size)
 {
-	int copied = 0;
+	bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
+	size_t copied = 0;
+
 	do {
-		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
-		int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
-		int space = __tty_buffer_request_room(port, goal, flags);
+		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 (~tb->flags & TTYB_NORMAL)
-			memset(flag_buf_ptr(tb, tb->used), flag, space);
-		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_fixed_flag);
 
-/**
- *	tty_insert_flip_string_flags	-	Add characters to the tty buffer
- *	@port: tty port
- *	@chars: characters
- *	@flags: flag bytes
- *	@size: size
- *
- *	Queue a series of bytes to the tty buffering. For each character
- *	the flags array indicates the status of the character. Returns the
- *	number added.
- */
+		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);
+		}
 
-int tty_insert_flip_string_flags(struct tty_port *port,
-		const unsigned char *chars, const char *flags, size_t size)
-{
-	int copied = 0;
-	do {
-		int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
-		int space = tty_buffer_request_room(port, goal);
-		struct tty_buffer *tb = port->buf.tail;
-		if (unlikely(space == 0))
-			break;
-		memcpy(char_buf_ptr(tb, tb->used), chars, space);
-		memcpy(flag_buf_ptr(tb, tb->used), flags, space);
 		tb->used += space;
 		copied += space;
 		chars += space;
-		flags += space;
+
 		/* There is a small chance that we need to split the data over
-		   several buffers. If this is the case we must loop */
+		 * several buffers. If this is the case we must loop.
+		 */
 	} while (unlikely(size > copied));
+
 	return copied;
 }
-EXPORT_SYMBOL(tty_insert_flip_string_flags);
+EXPORT_SYMBOL(__tty_insert_flip_string_flags);
 
 /**
- *	__tty_insert_flip_char   -	Add one character to the tty buffer
- *	@port: tty port
- *	@ch: character
- *	@flag: flag byte
+ * tty_prepare_flip_string	-	make room for characters
+ * @port: tty port
+ * @chars: return pointer for character write area
+ * @size: desired size
  *
- *	Queue a single byte to the tty buffering, with an optional flag.
- *	This is the slow path of tty_insert_flip_char.
- */
-int __tty_insert_flip_char(struct tty_port *port, unsigned char ch, char flag)
-{
-	struct tty_buffer *tb;
-	int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0;
-
-	if (!__tty_buffer_request_room(port, 1, flags))
-		return 0;
-
-	tb = port->buf.tail;
-	if (~tb->flags & TTYB_NORMAL)
-		*flag_buf_ptr(tb, tb->used) = flag;
-	*char_buf_ptr(tb, tb->used++) = ch;
-
-	return 1;
-}
-EXPORT_SYMBOL(__tty_insert_flip_char);
-
-/**
- *	tty_schedule_flip	-	push characters to ldisc
- *	@port: tty port to push from
+ * Prepare a block of space in the buffer for data.
  *
- *	Takes any pending buffers and transfers their ownership to the
- *	ldisc side of the queue. It then schedules those characters for
- *	processing by the line discipline.
- */
-
-void tty_schedule_flip(struct tty_port *port)
-{
-	struct tty_bufhead *buf = &port->buf;
-
-	/* paired w/ acquire in flush_to_ldisc(); ensures
-	 * flush_to_ldisc() sees buffer data.
-	 */
-	smp_store_release(&buf->tail->commit, buf->tail->used);
-	queue_work(system_unbound_wq, &buf->work);
-}
-EXPORT_SYMBOL(tty_schedule_flip);
-
-/**
- *	tty_prepare_flip_string		-	make room for characters
- *	@port: tty port
- *	@chars: return pointer for character write area
- *	@size: desired size
+ * 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!
  *
- *	Prepare a block of space in the buffer for data. Returns the length
- *	available and buffer pointer to the space which is now allocated and
- *	accounted for as ready for normal characters. 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.
  */
-
-int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
-		size_t size)
+size_t tty_prepare_flip_string(struct tty_port *port, u8 **chars, size_t size)
 {
-	int space = __tty_buffer_request_room(port, size, TTYB_NORMAL);
+	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 & TTYB_NORMAL)
+		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_* flags buffer
- *	@count:	number of bytes to process
+ * 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().
+ * 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
+ * Returns: the number of bytes processed.
  */
-int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
-			  char *f, int count)
+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(int, count, ld->tty->receive_room);
+		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);
 	}
@@ -468,14 +394,52 @@ int tty_ldisc_receive_buf(struct tty_ldisc *ld, const unsigned char *p,
 }
 EXPORT_SYMBOL_GPL(tty_ldisc_receive_buf);
 
-static int
-receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
+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)
 {
-	unsigned char *p = char_buf_ptr(head, head->read);
-	char	      *f = NULL;
-	int n;
+	u8 *p = char_buf_ptr(head, head->read);
+	const u8 *f = NULL;
+	size_t n;
 
-	if (~head->flags & TTYB_NORMAL)
+	if (head->flags)
 		f = flag_buf_ptr(head, head->read);
 
 	n = port->client_ops->receive_buf(port, p, f, count);
@@ -485,18 +449,16 @@ receive_buf(struct tty_port *port, struct tty_buffer *head, int count)
 }
 
 /**
- *	flush_to_ldisc
- *	@work: tty structure passed from work queue.
+ * 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.
+ * 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.
+ * The receive_buf() method is single threaded for each tty instance.
  *
- *	Locking: takes buffer lock to ensure single-threaded flip buffer
- *		 'consumer'
+ * 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);
@@ -507,7 +469,7 @@ static void flush_to_ldisc(struct work_struct *work)
 	while (1) {
 		struct tty_buffer *head = buf->head;
 		struct tty_buffer *next;
-		int count;
+		size_t count, rcvd;
 
 		/* Ldisc or user is trying to gain exclusive access */
 		if (atomic_read(&buf->priority))
@@ -530,41 +492,86 @@ static void flush_to_ldisc(struct work_struct *work)
 			continue;
 		}
 
-		count = receive_buf(port, head, count);
-		if (!count)
+		rcvd = receive_buf(port, head, count);
+		head->read += rcvd;
+		if (rcvd < count)
+			lookahead_bufs(port, head);
+		if (!rcvd)
 			break;
-		head->read += count;
+
+		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	-	terminal
- *	@port: tty port to push
+ * 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.
+ * 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.
+ * 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)
 {
-	tty_schedule_flip(port);
+	struct tty_bufhead *buf = &port->buf;
+
+	tty_flip_buffer_commit(buf->tail);
+	queue_work(system_dfl_wq, &buf->work);
 }
 EXPORT_SYMBOL(tty_flip_buffer_push);
 
 /**
- *	tty_buffer_init		-	prepare a tty buffer structure
- *	@tty: tty to initialise
+ * tty_insert_flip_string_and_push_buffer - add characters to the tty buffer and
+ *	push
+ * @port: tty port
+ * @chars: characters
+ * @size: size
  *
- *	Set up the initial state of the buffer management for a tty device.
- *	Must be called before the other tty buffer functions are used.
+ * 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_dfl_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;
@@ -581,13 +588,14 @@ void tty_buffer_init(struct tty_port *port)
 }
 
 /**
- *	tty_buffer_set_limit	-	change the tty buffer memory limit
- *	@port: tty port to change
+ * 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.
  *
- *	Change the tty buffer memory limit.
- *	Must be called before the other tty buffer functions are used.
+ * 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)
@@ -605,7 +613,7 @@ void tty_buffer_set_lock_subclass(struct tty_port *port)
 
 bool tty_buffer_restart_work(struct tty_port *port)
 {
-	return queue_work(system_unbound_wq, &port->buf.work);
+	return queue_work(system_dfl_wq, &port->buf.work);
 }
 
 bool tty_buffer_cancel_work(struct tty_port *port)