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Subject[PATCH] Futex update IV: use a waitqueue.
Date
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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