Subject: IDE locking problem
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Bartlomiej Zolnierkiewicz <B.Zolnierkiewicz@elka.pw.edu.pl>,
       Jens Axboe <axboe@suse.de>
Cc: linux-kernel mailing list <linux-kernel@vger.kernel.org>
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Date: 03 Aug 2003 10:42:29 +0200
Sender: linux-kernel-owner@vger.kernel.org
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Hi Alan & Bart !

While fixing my hotswap media-bay IDE controller for 2.6, I found
a locking problem with IDE (again ? :) in ide_unregister_hw. Basically
the problem is that it calls blk_cleanup_queue(), which is unsafe to
call with a lock held (it will call flush_workqueue() at one point).
Other side effect, flush_workqueue() will re-enable IRQs, thus allowing
us to get an IRQ while holding the spinlock -> double lock, but that's
just a side effect of calling flush_workqueue in that context.

So the call to blk_cleanup_queue() shall be moved outside of the
spinlock. I don't know much about the BIO details, is it possible
to first unregister_blkdev, then only call blk_cleanup_queue() ? That
would help making sure we don't get a request sneaking in ?

Ben.


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