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Date: Fri, 22 Dec 2000 14:19:29 +0100
From: Andrea Arcangeli <andrea@suse.de>
To: Andrew Morton <andrewm@uow.edu.au>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@redhat.com>
Subject: Re: Linux 2.2.19pre2
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In-Reply-To: <3A4303AC.C635F671@uow.edu.au>; from andrewm@uow.edu.au on Fri, Dec 22, 2000 at 06:33:00PM +1100
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On Fri, Dec 22, 2000 at 06:33:00PM +1100, Andrew Morton wrote:
> add_waitqueue_exclusive() and TASK_EXCLUSIVE, add a

There's no add_waitqueue_exclusive in my patch.

> Except for this bit, which looks slightly fatal:
> 
> 	/*
>          * We can drop the read-lock early if this
>          * is the only/last process.
>          */
>         if (next == head) {
>                  read_unlock(&waitqueue_lock);
>                  wake_up_process(p);
>                  goto out;
>         }
> 
> Once the waitqueue_lock has been dropped, the task at `p'
> is free to remove itself from the waitqueue and exit.  This
> CPU can then try to wake up a non-existent task, no?

Yes, that was an unlikely-to-happen SMP race I inerith from 2.2.18 and all
previous 2.2.x vanilla kernels. Thanks.

Andrea
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