Re: [PATCH] Memory leak in visor.c and ftdi_sio.c

[nardelli]

Ian Abbott wrote:
> On 04/06/2004 15:59, nardelli wrote:
>
> > Note that I have not verified any of the below on
> > hardware associated with drivers/usb/serial/ftdi_sio.c,
> > only with drivers/usb/serial/visor.c.  If anyone has
> > hardware for this device, I would appreciate your comments.
> >
> > A memory leak occurs in both drivers/usb/serial/ftdi_sio.c
> > and drivers/usb/serial/visor.c when the usb device is
> > unplugged while data is being written to the device.  This
> > patch should clear that up.
>
>
> The change to ftdi_sio.c looks correct to me.
>
> I made the original change to ftdi_sio.c to allocate the write urbs and 
> their transfer buffers dynamically (instead of using a preallocated 
> pool) and I copied that technique from visor.c!
>
> A related problem with the current implementation is that is easy to run 
> out of memory by running something similar to this:
>
>  # cat /dev/zero > /dev/ttyUSB0
>
> That affects both the ftdi_sio and visor drivers.

I believe that I have seen something similiar, but possibly not identical.
When writing alot (I used /dev/urandom instead of /dev/zero), it looks
like a very large percentage of buffers that are being allocated during
writes are not being freed.  One test I did indicated that 95% of buffers
were not being freed!  I briefly mention some info in
http://lkml.org/lkml/2004/5/25/72, but I wasn't going to go into detail
until I'd found out more info, and verified that my test procedure was
adequate.

My test is pretty simple, print out the address every time a buffer is
allocated, and print out the address every time a buffer is freed.  In
this case there is only one location where it is being allocated, but 3
(4 with patch I submitted) where it is being freed.  It's simply a matter
of running a command like the one below, and looking to see which addresses
are in there an odd number of times (i.e. allocated, but not freed).  Not a
perfect test, but hopefully not embarrassingly bad either.

cat /var/log/messages | egrep 'Allocated|Freed' | tr -s ' ' | cut -d ' ' -f 7 | sort | uniq -c | sort -n

I'm not sure why such a high percentage would not be freed, but hopefully I'll
figure it out in the next week or two, time permitting.

--
Joe Nardelli
jnardelli@xxxxxxxxxxxxxxxx
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