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Subject[PATCH 1/2] Futex minor fixes
Date
Hi Andrew, Ingo,

This was posted before, but dropped.

Name: Minor futex comment tweaks and cleanups
Author: Rusty Russell
Status: Tested on 2.6.0-test4-bk2

D: Changes:
D:
D: (1) don't return 0 from futex_wait if we are somehow
D: spuriously woken up, return -EINTR on any such case,
D:
D: (2) remove bogus comment about address no longer being in this
D: address space: we hold the mm lock, and __pin_page succeeded, so it
D: can't be true,
D:
D: (3) remove bogus comment about "get_user might fault and schedule",
D:
D: (4) remove list_empty check: we still hold the lock, so it can
D: never happen.
D:
D: (5) Single error exit path, and move __queue_me to the end (order
D: doesn't matter since we're inside the futex lock).

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .6150-linux-2.5.70-bk1/kernel/futex.c .6150-linux-2.5.70-bk1.updated/kernel/futex.c
--- .6150-linux-2.5.70-bk1/kernel/futex.c 2003-05-27 15:02:23.000000000 +1000
+++ .6150-linux-2.5.70-bk1.updated/kernel/futex.c 2003-05-28 16:42:45.000000000 +1000
@@ -312,7 +312,7 @@ static inline int futex_wait(unsigned lo
unsigned long time)
{
DECLARE_WAITQUEUE(wait, current);
- int ret = 0, curval;
+ int ret, curval;
struct page *page;
struct futex_q q;

@@ -322,55 +322,50 @@ static inline int futex_wait(unsigned lo

page = __pin_page(uaddr - offset);
if (!page) {
- unlock_futex_mm();
- return -EFAULT;
+ ret = -EFAULT;
+ goto unlock;
}
- __queue_me(&q, page, uaddr, offset, -1, NULL);
-
/*
- * Page is pinned, but may no longer be in this address space.
+ * Page is pinned, but may be a kernel address.
* It cannot schedule, so we access it with the spinlock held.
*/
if (get_user(curval, (int *)uaddr) != 0) {
- unlock_futex_mm();
ret = -EFAULT;
- goto out;
+ goto unlock;
}
+
if (curval != val) {
- unlock_futex_mm();
ret = -EWOULDBLOCK;
- goto out;
+ goto unlock;
}
- /*
- * The get_user() above might fault and schedule so we
- * cannot just set TASK_INTERRUPTIBLE state when queueing
- * ourselves into the futex hash. This code thus has to
- * rely on the futex_wake() code doing a wakeup after removing
- * the waiter from the list.
- */
+
+ __queue_me(&q, page, uaddr, offset, -1, NULL);
add_wait_queue(&q.waiters, &wait);
set_current_state(TASK_INTERRUPTIBLE);
- if (!list_empty(&q.list)) {
- unlock_futex_mm();
- time = schedule_timeout(time);
- }
+ unlock_futex_mm();
+
+ time = schedule_timeout(time);
+
set_current_state(TASK_RUNNING);
/*
* NOTE: we don't remove ourselves from the waitqueue because
* we are the only user of it.
*/
- if (time == 0) {
- ret = -ETIMEDOUT;
- goto out;
- }
- if (signal_pending(current))
- ret = -EINTR;
-out:
- /* Were we woken up anyway? */
+
+ /* Were we woken up (and removed from queue)? Always return
+ * success when this happens. */
if (!unqueue_me(&q))
ret = 0;
+ else if (time == 0)
+ ret = -ETIMEDOUT;
+ else
+ ret = -EINTR;
+
put_page(q.page);
+ return ret;

+unlock:
+ unlock_futex_mm();
return ret;
}

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