Messages in this thread | | | Date | Sun, 14 Nov 2004 23:24:43 -0500 | From | Chuck Ebbert <> | Subject | Re: Futex queue_me/get_user ordering (was: 2.6.10-rc1-mm5 [u]) |
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On Sun, 14 Nov 2004 at 09:00:23 +0000 Emergency Services Jamie Lokier wrote:
>+ * The basic logical guarantee of a futex is that it blocks ONLY >+ * if cond(var) is known to be true at the time of blocking, for >+ * any cond. If we queued after testing *uaddr, that would open >+ * a race condition where we could block indefinitely with >+ * cond(var) false, which would violate the guarantee. >+ * >+ * A consequence is that futex_wait() can return zero and absorb >+ * a wakeup when *uaddr != val on entry to the syscall. This is >+ * rare, but normal.
Why can't it absorb a wakeup and still return -EAGAIN when this happens?
IOW why not apply this patch to the original code?
================================================================================ return -EINTR; out_unqueue: - /* If we were woken (and unqueued), we succeeded, whatever. */ - if (!unqueue_me(&q)) - ret = 0; + unqueue_me(&q); /* ignore result from unqueue */ out_release_sem: up_read(¤t->mm->mmap_sem); return ret; ================================================================================
...and what is "Emergency Services", BTW?
--Chuck Ebbert 14-Nov-04 21:28:56 - 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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