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Subject[PATCH 3/4] firewire: net: replace lists by counters
The current transmit code does not at all make use of
- fwnet_device.packet_list
and only very limited use of
- fwnet_device.broadcasted_list,
- fwnet_device.queued_packets.
Their current function is to track whether the TX soft-IRQ finished
dealing with an skb when the AT-req tasklet takes over, and to discard
pending tx datagrams (if there are any) when the local node is removed.

The latter does actually contain a race condition bug with TX soft-IRQ
and AT-req tasklet.

Instead of these lists and the corresponding link in fwnet_packet_task,
- a flag in fwnet_packet_task to track whether fwnet_tx is done,
- a counter of queued datagrams in fwnet_device
do the job as well.

The above mentioned theoretic race condition is resolved by letting
fwnet_remove sleep until all datagrams were flushed. It may sleep
almost arbitrarily long since fwnet_remove is executed in the context of
a multithreaded (concurrency managed) workqueue.

The type of max_payload is changed to u16 here to avoid waste in struct
fwnet_packet_task. This value cannot exceed 4096 per IEEE 1394:2008
table 16-18 (or 32678 per specification of packet headers, if there is
ever going to be something else than beta mode).

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
---
drivers/firewire/net.c | 73 +++++++++++++++--------------------------
1 file changed, 26 insertions(+), 47 deletions(-)
Index: b/drivers/firewire/net.c
===================================================================
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -7,6 +7,7 @@
*/

#include <linux/bug.h>
+#include <linux/delay.h>
#include <linux/device.h>
#include <linux/ethtool.h>
#include <linux/firewire.h>
@@ -170,15 +171,8 @@ struct fwnet_device {
struct fw_address_handler handler;
u64 local_fifo;

- /* List of packets to be sent */
- struct list_head packet_list;
- /*
- * List of packets that were broadcasted. When we get an ISO interrupt
- * one of them has been sent
- */
- struct list_head broadcasted_list;
- /* List of packets that have been sent but not yet acked */
- struct list_head sent_list;
+ /* Number of tx datagrams that have been queued but not yet acked */
+ int queued_datagrams;

struct list_head peer_list;
struct fw_card *card;
@@ -196,7 +190,7 @@ struct fwnet_peer {
unsigned pdg_size; /* pd_list size */

u16 datagram_label; /* outgoing datagram label */
- unsigned max_payload; /* includes RFC2374_FRAG_HDR_SIZE overhead */
+ u16 max_payload; /* includes RFC2374_FRAG_HDR_SIZE overhead */
int node_id;
int generation;
unsigned speed;
@@ -204,22 +198,18 @@ struct fwnet_peer {

/* This is our task struct. It's used for the packet complete callback. */
struct fwnet_packet_task {
- /*
- * ptask can actually be on dev->packet_list, dev->broadcasted_list,
- * or dev->sent_list depending on its current state.
- */
- struct list_head pt_link;
struct fw_transaction transaction;
struct rfc2734_header hdr;
struct sk_buff *skb;
struct fwnet_device *dev;

int outstanding_pkts;
- unsigned max_payload;
u64 fifo_addr;
u16 dest_node;
+ u16 max_payload;
u8 generation;
u8 speed;
+ u8 enqueued;
};

/*
@@ -916,9 +906,9 @@ static void fwnet_transmit_packet_done(s
ptask->outstanding_pkts--;

/* Check whether we or the networking TX soft-IRQ is last user. */
- free = (ptask->outstanding_pkts == 0 && !list_empty(&ptask->pt_link));
+ free = (ptask->outstanding_pkts == 0 && ptask->enqueued);
if (free)
- list_del(&ptask->pt_link);
+ dev->queued_datagrams--;

if (ptask->outstanding_pkts == 0) {
dev->netdev->stats.tx_packets++;
@@ -987,9 +977,9 @@ static void fwnet_transmit_packet_failed
ptask->outstanding_pkts = 0;

/* Check whether we or the networking TX soft-IRQ is last user. */
- free = !list_empty(&ptask->pt_link);
+ free = ptask->enqueued;
if (free)
- list_del(&ptask->pt_link);
+ dev->queued_datagrams--;

dev->netdev->stats.tx_dropped++;
dev->netdev->stats.tx_errors++;
@@ -1070,9 +1060,11 @@ static int fwnet_send_packet(struct fwne
spin_lock_irqsave(&dev->lock, flags);

/* If the AT tasklet already ran, we may be last user. */
- free = (ptask->outstanding_pkts == 0 && list_empty(&ptask->pt_link));
+ free = (ptask->outstanding_pkts == 0 && !ptask->enqueued);
if (!free)
- list_add_tail(&ptask->pt_link, &dev->broadcasted_list);
+ ptask->enqueued = true;
+ else
+ dev->queued_datagrams--;

spin_unlock_irqrestore(&dev->lock, flags);

@@ -1087,9 +1079,11 @@ static int fwnet_send_packet(struct fwne
spin_lock_irqsave(&dev->lock, flags);

/* If the AT tasklet already ran, we may be last user. */
- free = (ptask->outstanding_pkts == 0 && list_empty(&ptask->pt_link));
+ free = (ptask->outstanding_pkts == 0 && !ptask->enqueued);
if (!free)
- list_add_tail(&ptask->pt_link, &dev->sent_list);
+ ptask->enqueued = true;
+ else
+ dev->queued_datagrams--;

spin_unlock_irqrestore(&dev->lock, flags);

@@ -1351,10 +1345,12 @@ static netdev_tx_t fwnet_tx(struct sk_bu
max_payload += RFC2374_FRAG_HDR_SIZE;
}

+ dev->queued_datagrams++;
+
spin_unlock_irqrestore(&dev->lock, flags);

ptask->max_payload = max_payload;
- INIT_LIST_HEAD(&ptask->pt_link);
+ ptask->enqueued = 0;

fwnet_send_packet(ptask);

@@ -1500,14 +1496,9 @@ static int fwnet_probe(struct device *_d
dev->broadcast_rcv_context = NULL;
dev->broadcast_xmt_max_payload = 0;
dev->broadcast_xmt_datagramlabel = 0;
-
dev->local_fifo = FWNET_NO_FIFO_ADDR;
-
- INIT_LIST_HEAD(&dev->packet_list);
- INIT_LIST_HEAD(&dev->broadcasted_list);
- INIT_LIST_HEAD(&dev->sent_list);
+ dev->queued_datagrams = 0;
INIT_LIST_HEAD(&dev->peer_list);
-
dev->card = card;
dev->netdev = net;

@@ -1565,7 +1556,7 @@ static int fwnet_remove(struct device *_
struct fwnet_peer *peer = dev_get_drvdata(_dev);
struct fwnet_device *dev = peer->dev;
struct net_device *net;
- struct fwnet_packet_task *ptask, *pt_next;
+ int i;

mutex_lock(&fwnet_device_mutex);

@@ -1583,21 +1574,9 @@ static int fwnet_remove(struct device *_
dev->card);
fw_iso_context_destroy(dev->broadcast_rcv_context);
}
- list_for_each_entry_safe(ptask, pt_next,
- &dev->packet_list, pt_link) {
- dev_kfree_skb_any(ptask->skb);
- kmem_cache_free(fwnet_packet_task_cache, ptask);
- }
- list_for_each_entry_safe(ptask, pt_next,
- &dev->broadcasted_list, pt_link) {
- dev_kfree_skb_any(ptask->skb);
- kmem_cache_free(fwnet_packet_task_cache, ptask);
- }
- list_for_each_entry_safe(ptask, pt_next,
- &dev->sent_list, pt_link) {
- dev_kfree_skb_any(ptask->skb);
- kmem_cache_free(fwnet_packet_task_cache, ptask);
- }
+ for (i = 0; dev->queued_datagrams && i < 5; i++)
+ ssleep(1);
+ WARN_ON(dev->queued_datagrams);
list_del(&dev->dev_link);

free_netdev(net);
--
Stefan Richter
-=====-==-=- =-== --===
http://arcgraph.de/sr/


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