From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [Hdaps-devel] Re: HDAPS, Need to park the head for real
Date: Thu, 25 Aug 2005 11:57:47 +0100
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To: Jon Escombe <lists@dresco.co.uk>
Cc: Jens Axboe <axboe@suse.de>, Alejandro Bonilla Beeche <abonilla@linuxwireless.org>, linux-kernel <linux-kernel@vger.kernel.org>, hdaps devel <hdaps-devel@lists.sourceforge.net>, linux-ide@vger.kernel.org

You need the kernel side timeout. Consider this case

One page of memory holds the parking code
A second page is swapped to disk and holds the resume code

You park the disk
You wakeup
You got to page in the resume code

So you really do want the kernel helping to avoid a deadlock

@@ -1661,6 +1671,9 @@
                where = ELEVATOR_INSERT_FRONT;
                rq->flags |= REQ_PREEMPT;
        }
+       if (action == ide_next)
+               where = ELEVATOR_INSERT_FRONT;
+
        __elv_add_request(drive->queue, rq, where, 0);
        ide_do_request(hwgroup, IDE_NO_IRQ);
        spin_unlock_irqrestore(&ide_lock, flags);

Also puzzles me- why is this needed ?