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SubjectRe: [PATCH 2.6.17-rc5] ieee1394_core: switch to kthread API
On Sun, 28 May 2006 18:43:52 +0200 (CEST)
Stefan Richter <stefanr@s5r6.in-berlin.de> wrote:

We end up with:

:static void queue_packet_complete(struct hpsb_packet *packet)
:{
: if (packet->no_waiter) {
: hpsb_free_packet(packet);
: return;
: }
: if (packet->complete_routine != NULL) {
: skb_queue_tail(&hpsbpkt_queue, packet->skb);
: wake_up_process(khpsbpkt_thread);
: }
: return;
:}
:
:static int hpsbpkt_thread(void *__hi)
:{
: struct sk_buff *skb;
: struct hpsb_packet *packet;
: void (*complete_routine)(void*);
: void *complete_data;
:
: current->flags |= PF_NOFREEZE;
:
: while (!kthread_should_stop()) {
: while ((skb = skb_dequeue(&hpsbpkt_queue)) != NULL) {
: packet = (struct hpsb_packet *)skb->data;
:
: complete_routine = packet->complete_routine;
: complete_data = packet->complete_data;
:
: packet->complete_routine = packet->complete_data = NULL;
:
: complete_routine(complete_data);
: }

There's a race here.

: set_current_state(TASK_INTERRUPTIBLE );
: schedule();
: }
:
: return 0;
:}

If queue_packet_complete() is called on another CPU in that window, there
will be a new skb queued and we'll miss the wakeup.

I used skb_peek() in the below fix, but there are other ways, perhaps..


--- devel/drivers/ieee1394/ieee1394_core.c~ieee1394_core-switch-to-kthread-api-fix 2006-05-29 15:42:30.000000000 -0700
+++ devel-akpm/drivers/ieee1394/ieee1394_core.c 2006-05-29 15:42:40.000000000 -0700
@@ -1001,7 +1001,6 @@ void abort_timedouts(unsigned long __opa
static struct task_struct *khpsbpkt_thread;
static struct sk_buff_head hpsbpkt_queue;

-
static void queue_packet_complete(struct hpsb_packet *packet)
{
if (packet->no_waiter) {
@@ -1036,10 +1035,11 @@ static int hpsbpkt_thread(void *__hi)
complete_routine(complete_data);
}

- set_current_state(TASK_INTERRUPTIBLE );
- schedule();
+ set_current_state(TASK_INTERRUPTIBLE);
+ if (!skb_peek(&hpsbpkt_queue))
+ schedule();
+ __set_current_state(TASK_RUNNING);
}
-
return 0;
}

_
-
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