Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Rusty Russell <> | Subject | [PATCH 1/2] Futex minor fixes | Date | Tue, 26 Aug 2003 13:05:56 +1000 |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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