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    SubjectRe: Ooops when working with USB MIDI (2.6.33.1)
    At Thu, 08 Apr 2010 12:00:11 +0200,
    Clemens Ladisch wrote:
    >
    > Tvrtko Ursulin wrote:
    > > I had TuxGuitar running and an external USB MIDI device, which I then
    > > turned off, on, and exited TuxGuitar at which point there was this oops.
    > > ...
    > > [321182.618342] IP: [<ffffffff81375d65>] _raw_spin_lock_irq+0x15/0x30
    > > [321182.618449] [<ffffffffa01e2fca>] ? snd_usbmidi_output_drain+0x7a/0x100 [snd_usb_lib]
    > > [321182.618462] [<ffffffffa01b7699>] ? snd_rawmidi_drain_output+0x119/0x180 [snd_rawmidi]
    >
    > I think that bug was introduced by this commit:
    > http://git.kernel.org/linus/7a17daae8ed71bf3259d905a4fc48a5b424fa935
    > which causes the driver to free many internal data structures when
    > they might still be in use by userspace.
    >
    > Please try to revert it.
    >
    > I think a proper fix would be to free the URBs/buffers but not the
    > driver's data structures.
    >
    > Takashi, do you remember what the original problem was?

    Well, I have only a vague memory -- it's a similar scenario that some app
    still accessing after disconnection. The URB can't be handled after
    the disconnection is finished.

    I think the patch below might fix in this case. You can try it
    instead of reverting the commit above.


    thanks,

    Takashi

    ---
    diff --git a/sound/usb/usbmidi.c b/sound/usb/usbmidi.c
    index 2c59afd..81c8d85 100644
    --- a/sound/usb/usbmidi.c
    +++ b/sound/usb/usbmidi.c
    @@ -986,6 +986,8 @@ static void snd_usbmidi_output_drain(struct snd_rawmidi_substream *substream)
    DEFINE_WAIT(wait);
    long timeout = msecs_to_jiffies(50);

    + if (ep->umidi->disconnected)
    + return;
    /*
    * The substream buffer is empty, but some data might still be in the
    * currently active URBs, so we have to wait for those to complete.
    @@ -1275,6 +1277,11 @@ void snd_usbmidi_disconnect(struct list_head* p)
    snd_usbmidi_in_endpoint_delete(ep->in);
    ep->in = NULL;
    }
    + ep->active_urbs = 0;
    + if (ep->drain_urbs) {
    + ep->drain_urbs = 0;
    + wake_up(&ep->drain_wait);
    + }
    }
    del_timer_sync(&umidi->error_timer);
    }

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