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    SubjectRe: [PATCH] usb_storage: make usb-stor-scan task non-freezable
    On Tue, 26 Jul 2011, Seth Forshee wrote:

    > On Sat, Jul 23, 2011 at 09:56:15PM -0400, Alan Stern wrote:
    > > On Sat, 23 Jul 2011, Seth Forshee wrote:
    > >
    > > > After experimenting with this device more I came to the conclusion that
    > > > the normal behavior with this machine is for the card reader to be
    > > > disconnected from the USB bus unless there's a card in the slot. During
    > > > a normal boot with an empty card slot the card reader never shows up on
    > > > the bus.
    > >
    > > Weird. Then the reader would never be usable. Unless it connects
    > > itself to the bus when a card is inserted?
    >
    > Yes, the reader is connected to the bus when a card is inserted. Remove
    > the card and it disappears again.

    That's the first time I've heard of such a thing.

    > > > The only solution I've come up with is to leave usb-stor-scan freezable
    > > > without allowing it to actually freeze. We can request a fake signal be
    > > > sent when freezing and use interruptible sleep to abort the wait early
    > > > and finish up the thread's processing. This is implemented in the patch
    > > > below. Does this approach look reasonable? It's rather subtle, but it
    > > > does seem to work. I done numerous S4 cycles with and without a card
    > > > inserted and didn't get any failures.
    > >
    > > This runs the risk of failing to suspend if scanning takes too long.
    >
    > It may increase the exposure to that risk, but really the risk is
    > already there.

    True. Once the scanning begins there's no way to freeze the thread,
    even in the current code.

    > > On the other hand, many systems nowadays use async scanning anyway.
    > > And that combination of events isn't too likely to happen, whereas
    > > you're facing a real problem right now. So I guess this is okay.
    >
    > Great, thanks.
    >
    > Will the patch get picked up from my previous email, or do I need to
    > resend it?

    You should resend it to Greg, and you can add

    Acked-by: Alan Stern <stern@rowland.harvard.edu>

    Alan Stern



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