0007-tty-n_r3964-for-rx_blocks-use-a-real-kernel-list.patch

From c711e9d95e2fbc99dc88c0797f58194ade169258 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Thu, 24 Jan 2019 16:04:54 +0100
Subject: [PATCH 07/15] tty: n_r3964: for rx_blocks, use a real kernel list

The rx blocks have a hand-rolled linked list structure, use a "normal"
kernel list structure instead, making the code smaller and easier to
understand and verify that it really does what we think it should be
doing.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/n_r3964.c |   67 +++++++++-----------------------------------------
 1 file changed, 13 insertions(+), 54 deletions(-)

--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -132,8 +132,7 @@ struct rx_block_header {
 	unsigned char *data;	/* usually data is located immediately
 				 * behind this struct */
 	unsigned int locks;	/* only used in rx_buffer */
-
-	struct rx_block_header *next;
+	struct list_head node;
 };
 
 /* Header of received block in tx_buf: */
@@ -169,8 +168,7 @@ struct r3964_info {
 	unsigned char *rx_buf;            /* ring buffer */
 	unsigned char *tx_buf;
 
-	struct rx_block_header *rx_first;
-	struct rx_block_header *rx_last;
+	struct list_head rx_blocks;
 	struct list_head tx_blocks;
 	unsigned int tx_position;
         unsigned int rx_position;
@@ -355,71 +353,32 @@ static void add_rx_queue(struct r3964_in
 	unsigned long flags;
 
 	spin_lock_irqsave(&pInfo->lock, flags);
-
-	pHeader->next = NULL;
-
-	if (pInfo->rx_last == NULL) {
-		pInfo->rx_first = pInfo->rx_last = pHeader;
-	} else {
-		pInfo->rx_last->next = pHeader;
-		pInfo->rx_last = pHeader;
-	}
-	pInfo->blocks_in_rx_queue++;
-
+	list_add_tail(&pHeader->node, &pInfo->rx_blocks);
 	spin_unlock_irqrestore(&pInfo->lock, flags);
-
-	TRACE_Q("add_rx_queue: %p, length = %d, rx_first = %p, count = %d",
-		pHeader, pHeader->length,
-		pInfo->rx_first, pInfo->blocks_in_rx_queue);
 }
 
 static void remove_from_rx_queue(struct r3964_info *pInfo,
 				 struct rx_block_header *pHeader)
 {
+	struct rx_block_header *pFind, *tmp;
 	unsigned long flags;
-	struct rx_block_header *pFind;
 
 	if (pHeader == NULL)
 		return;
 
-	TRACE_Q("remove_from_rx_queue: rx_first = %p, rx_last = %p, count = %d",
-		pInfo->rx_first, pInfo->rx_last, pInfo->blocks_in_rx_queue);
-	TRACE_Q("remove_from_rx_queue: %p, length %u",
-		pHeader, pHeader->length);
-
 	spin_lock_irqsave(&pInfo->lock, flags);
-
-	if (pInfo->rx_first == pHeader) {
-		/* Remove the first block in the linked list: */
-		pInfo->rx_first = pHeader->next;
-
-		if (pInfo->rx_first == NULL) {
-			pInfo->rx_last = NULL;
-		}
-		pInfo->blocks_in_rx_queue--;
-	} else {
-		/* Find block to remove: */
-		for (pFind = pInfo->rx_first; pFind; pFind = pFind->next) {
-			if (pFind->next == pHeader) {
-				/* Got it. */
-				pFind->next = pHeader->next;
-				pInfo->blocks_in_rx_queue--;
-				if (pFind->next == NULL) {
-					/* Oh, removed the last one! */
-					pInfo->rx_last = pFind;
-				}
-				break;
-			}
+	list_for_each_entry_safe(pFind, tmp, &pInfo->rx_blocks, node) {
+		if (pFind == pHeader) {
+			/* Got it. */
+			list_del(&pFind->node);
+			pInfo->blocks_in_rx_queue--;
+			goto exit;
 		}
 	}
-
+exit:
 	spin_unlock_irqrestore(&pInfo->lock, flags);
 
 	kfree(pHeader);
-	TRACE_M("remove_from_rx_queue - kfree %p", pHeader);
-
-	TRACE_Q("remove_from_rx_queue: rx_first = %p, rx_last = %p, count = %d",
-		pInfo->rx_first, pInfo->rx_last, pInfo->blocks_in_rx_queue);
 }
 
 static void put_char(struct r3964_info *pInfo, unsigned char ch)
@@ -582,7 +541,7 @@ static void on_receive_block(struct r396
 	pBlock->length = length;
 	pBlock->data = ((unsigned char *)pBlock) + sizeof(*pBlock);
 	pBlock->locks = 0;
-	pBlock->next = NULL;
+	INIT_LIST_HEAD(&pBlock->node);
 
 	memcpy(pBlock->data, pInfo->rx_buf, length);
 
@@ -1047,7 +1006,7 @@ static int r3964_open(struct tty_struct
 	mutex_init(&pInfo->read_lock);
 	pInfo->tty = tty;
 	pInfo->priority = R3964_MASTER;
-	pInfo->rx_first = pInfo->rx_last = NULL;
+	INIT_LIST_HEAD(&pInfo->rx_blocks);
 	INIT_LIST_HEAD(&pInfo->tx_blocks);
 	pInfo->rx_position = 0;
 	pInfo->tx_position = 0;