Re: [linux-usb-devel] [PATCH] visor: Fix Oops on disconnect

From: Greg KH (greg_at_kroah.com)
Date: 05/24/04

  • Next message: Greg KH: "Re: [linux-usb-devel] [PATCH] visor: Fix Oops on disconnect"
    Date:	Mon, 24 May 2004 13:06:11 -0700
    To: nardelli <jnardelli@infosciences.com>
    
    

    On Mon, May 24, 2004 at 03:38:58PM -0400, nardelli wrote:
    > nardelli wrote:
    > >
    > >One more question - my system does not really like it when I redirect
    > >/dev/urandom
    > >to either the first or second port. I know that it obviosuly makes no
    > >sense to
    > >do such a thing, but is it expected that there should be no problems
    > >associated
    > >with this. I'm not finished testing, so I'm not sure how severe a problem
    > >develops.
    > >I'll report in when I know more about this.
    > >
    >
    > Here's some preliminary info:
    >
    > 1) Whether writing to the 1st or 2nd port, the machine hangs pretty badly
    > after catting /dev/urandom for more than 1 second or two. This continues
    > even after catting has stopped, and the device has been disconnected. This
    > smells like some type of resource leak, probably memory, to me.

    Which machine dies? The pilot or the Linux box?

    > 2) I've included an Oops when writing to the 1st serial port, showing some
    > difficulty allocating memory.

    So we ran out of memory? Not good.

    > 3) After looking at visor_write(), I was a bit surprised to see it
    > allocating its own urb and buffer, while I thought it would be using
    > the ones that were allocated in usb-serial.usb_serial_probe(). After
    > looking at other serial devices that use usb_submit_urb() in their
    > write() functions, I found that the following used the buffers/urb
    > allocated for them:
    >
    > cyberjack, digi_acceleport, generic, io_ti, ipaq, ir-usb, keyspan_pda,
    > kobil_sct, mct_u232, omninet, pl2303, safe_serial
    >
    > while I found that the following created their own (some for each write):
    >
    > empeg, ftdi_sio, keyspan, kl5kusb105, visor, whiteheat
    >
    > I'm not so sure about:
    > io_edgeport

    It uses it's own buffers from what I remember.

    > Is this expected behavior, or am I just missing something here?

    Expected, not all of the usb-serial drivers have to do the same thing,
    as they operate on very different types of hardware.

    > It would seem like reusing the buffer and urb would be advantageous,
    > but there may be more issues here than I am aware of.

    Reusing the buffer and urb is _slow_. The visor driver creates a new
    buffer for every call to write. It is entirely possible that you can
    starve the kernel of memory by sending it the output of a raw device
    node, as that data comes faster than the USB data can be sent.

    But this is a different problem from the one you originally set out to
    fix, how about sending a new patch for the treo disconnect problem, and
    then we can work on the next issues.

    thanks,

    greg k-h
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