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    SubjectRe: IDE locking problem
    On Sun, Aug 03 2003, Jens Axboe wrote:
    > On Sun, Aug 03 2003, Benjamin Herrenschmidt wrote:
    > > 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.
    >
    > Irk someone made blk_cleanup_queue() non-atomic. I blame Andrew. And now
    > it looks like it's impossible to make it atomic again :/. Not very nice,
    > imo it's preferable to keep such unregister functions atomic.
    >
    > > 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
    >
    > That should work, yes.
    >
    > > would help making sure we don't get a request sneaking in ?
    >
    > Hmm not really, there's still a chance that could happen.

    and unregister_blkdev() itself isn't even atomic. So I guess IDE does
    need fixing anyways.

    --
    Jens Axboe

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