X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=drivers%2Ftty%2Ftty_buffer.c;h=c043136fbe5198cf0a7a8704254fc28763ecd0b9;hb=1a7b0ecbbc1219895f48934ff5549a3594db3480;hp=fb042b9a8d6881c06bd2812a4808dd6c73f43aac;hpb=0f56bd2f6a97d8b0eb5c8f9bc04b83a6c16d1d48;p=firefly-linux-kernel-4.4.55.git

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index fb042b9a8d68..c043136fbe51 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -28,6 +28,52 @@
  */
 #define TTYB_MEM_LIMIT	65536
 
+/*
+ * 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
+ */
+
+#define TTY_BUFFER_PAGE	(((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)
+
+
+/**
+ *	tty_buffer_lock_exclusive	-	gain exclusive access to buffer
+ *	tty_buffer_unlock_exclusive	-	release exclusive access
+ *
+ *	@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.
+ *
+ *	On release, the buffer work is restarted if there is data in the
+ *	flip buffer
+ */
+
+void tty_buffer_lock_exclusive(struct tty_port *port)
+{
+	struct tty_bufhead *buf = &port->buf;
+
+	atomic_inc(&buf->priority);
+	mutex_lock(&buf->lock);
+}
+
+void tty_buffer_unlock_exclusive(struct tty_port *port)
+{
+	struct tty_bufhead *buf = &port->buf;
+	int restart;
+
+	restart = buf->head->commit != buf->head->read;
+
+	atomic_dec(&buf->priority);
+	mutex_unlock(&buf->lock);
+	if (restart)
+		queue_work(system_unbound_wq, &buf->work);
+}
 
 /**
  *	tty_buffer_space_avail	-	return unused buffer space
@@ -150,28 +196,6 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
 		llist_add(&b->free, &buf->free);
 }
 
-/**
- *	__tty_buffer_flush		-	flush full tty buffers
- *	@tty: tty to flush
- *
- *	flush all the buffers containing receive data. Caller must
- *	hold the buffer lock and must have ensured no parallel flush to
- *	ldisc is running.
- */
-
-static void __tty_buffer_flush(struct tty_port *port)
-{
-	struct tty_bufhead *buf = &port->buf;
-	struct tty_buffer *next;
-
-	while ((next = buf->head->next) != NULL) {
-		tty_buffer_free(port, buf->head);
-		buf->head = next;
-	}
-	WARN_ON(buf->head != buf->tail);
-	buf->head->read = buf->head->commit;
-}
-
 /**
  *	tty_buffer_flush		-	flush full tty buffers
  *	@tty: tty to flush
@@ -180,7 +204,7 @@ static void __tty_buffer_flush(struct tty_port *port)
  *	being processed by flush_to_ldisc then we defer the processing
  *	to that function
  *
- *	Locking: takes flush_mutex to ensure single-threaded flip buffer
+ *	Locking: takes buffer lock to ensure single-threaded flip buffer
  *		 'consumer'
  */
 
@@ -188,13 +212,18 @@ void tty_buffer_flush(struct tty_struct *tty)
 {
 	struct tty_port *port = tty->port;
 	struct tty_bufhead *buf = &port->buf;
+	struct tty_buffer *next;
 
-	buf->flushpending = 1;
+	atomic_inc(&buf->priority);
 
-	mutex_lock(&buf->flush_mutex);
-	__tty_buffer_flush(port);
-	buf->flushpending = 0;
-	mutex_unlock(&buf->flush_mutex);
+	mutex_lock(&buf->lock);
+	while ((next = buf->head->next) != NULL) {
+		tty_buffer_free(port, buf->head);
+		buf->head = next;
+	}
+	buf->head->read = buf->head->commit;
+	atomic_dec(&buf->priority);
+	mutex_unlock(&buf->lock);
 }
 
 /**
@@ -400,7 +429,7 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
  *
  *	The receive_buf method is single threaded for each tty instance.
  *
- *	Locking: takes flush_mutex to ensure single-threaded flip buffer
+ *	Locking: takes buffer lock to ensure single-threaded flip buffer
  *		 'consumer'
  */
 
@@ -419,14 +448,14 @@ static void flush_to_ldisc(struct work_struct *work)
 	if (disc == NULL)
 		return;
 
-	mutex_lock(&buf->flush_mutex);
+	mutex_lock(&buf->lock);
 
 	while (1) {
 		struct tty_buffer *head = buf->head;
 		int count;
 
-		/* Ldisc or user is trying to flush the buffers. */
-		if (buf->flushpending)
+		/* Ldisc or user is trying to gain exclusive access */
+		if (atomic_read(&buf->priority))
 			break;
 
 		count = head->commit - head->read;
@@ -443,7 +472,7 @@ static void flush_to_ldisc(struct work_struct *work)
 			break;
 	}
 
-	mutex_unlock(&buf->flush_mutex);
+	mutex_unlock(&buf->lock);
 
 	tty_ldisc_deref(disc);
 }
@@ -499,13 +528,12 @@ void tty_buffer_init(struct tty_port *port)
 {
 	struct tty_bufhead *buf = &port->buf;
 
-	mutex_init(&buf->flush_mutex);
+	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->memory_used, 0);
-	buf->flushpending = 0;
+	atomic_set(&buf->priority, 0);
 	INIT_WORK(&buf->work, flush_to_ldisc);
 }
-