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

[Greg KH]

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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