[PATCH] Futex update IV: use a waitqueue.

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Name: Use a waitqueue, rather than a task ptr
Author: Rusty Russell
Status: Tested in 2.5.20
Depends: Futex/copy-from-user.patch.gz

D: This turns the simple task pointer into a waitqueue, which is
D: needed for the poll() patch.

diff -urN -I \$.*\$ --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.20.18954/kernel/futex.c linux-2.5.20.18954.updated/kernel/futex.c
--- linux-2.5.20.18954/kernel/futex.c Thu Jun 6 17:12:20 2002
+++ linux-2.5.20.18954.updated/kernel/futex.c Thu Jun 6 17:13:05 2002
@@ -49,7 +49,7 @@
    the relevent ones (hashed queues may be shared) */
 struct futex_q {
         struct list_head list;
- struct task_struct *task;
+ wait_queue_head_t waiters;
         /* Page struct and offset within it. */
         struct page *page;
         unsigned int offset;
@@ -69,6 +69,11 @@
         return &futex_queues[hash_long(h, FUTEX_HASHBITS)];
 }
 
+static inline void tell_waiter(struct futex_q *q)
+{
+ wake_up_all(&q->waiters);
+}
+
 static int futex_wake(struct list_head *head,
                       struct page *page,
                       unsigned int offset,
@@ -83,7 +88,7 @@
 
                 if (this->page == page && this->offset == offset) {
                         list_del_init(i);
- wake_up_process(this->task);
+ tell_waiter(this);
                         num_woken++;
                         if (num_woken >= num) break;
                 }
@@ -94,11 +99,12 @@
 
 /* Add at end to avoid starvation */
 static inline void queue_me(struct list_head *head,
+ wait_queue_t *wait,
                             struct futex_q *q,
                             struct page *page,
                             unsigned int offset)
 {
- q->task = current;
+ add_wait_queue(&q->waiters, wait);
         q->page = page;
         q->offset = offset;
 
@@ -150,10 +156,11 @@
 {
         int curval;
         struct futex_q q;
+ DECLARE_WAITQUEUE(wait, current);
         int ret = 0;
 
         set_current_state(TASK_INTERRUPTIBLE);
- queue_me(head, &q, page, offset);
+ queue_me(head, &wait, &q, page, offset);
 
         /* Page is pinned, but may no longer be in this address space. */
         if (get_user(curval, uaddr) != 0) {

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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