linux-kernel - Re: usbip: sometimes stalls at kernel

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Message-ID: <4D0FD725.5000609@vozeler.com>
Date:	Mon, 20 Dec 2010 23:22:29 +0100
From:	Max Vozeler <max@...eler.com>
To:	Németh Márton <nm127@...email.hu>
CC:	gregkh <gregkh@...e.de>, devel@...verdev.osuosl.org,
	LKML <linux-kernel@...r.kernel.org>,
	usbip-devel@...ts.sourceforge.net
Subject: Re: usbip: sometimes stalls at kernel_recvmsg()

Hi Németh,

On 17.12.2010 06:45, Németh Márton wrote:
>>> Németh Márton wrote:
>>>> I'm working with usbip and I sometimes see a stall when I run
>>>> the "lsusb" command from the userspace. 
>>
>> Does it eventually recover?
> 
> No, it doesn't. After 120 seconds messages are printed in dmesg
> that the "lsusb" process is blocked more than 120 seconds.

Can you describe the sequence of events which
happened before the hang?

Was the device detached before or during lsusb?

Perhaps try echo t > /proc/sysrq-trigger to see
where exactly lsusb gets stuck.

I found processes can get stuck in usb_kill_urb 
if they tried to unlink an URB, but the unlink
request was not answered before detach.

Perhaps this is related. I am attaching a patch
which fixes that bug for me, perhaps you could 
try if it makes a difference?

>>>> I added some debug messages
>>>> and it seems that the kernel_recvmsg() in
>>>> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=drivers/staging/usbip/usbip_common.c;h=210ef16bab8d271a52e5d36cd1994aad57ad99e1;hb=HEAD
>>>>
>>>> This is the only place I could find where the TCP messages are arriving in
>>>> the usbip code.
>>>>
>>>> What happens if a message does not arrive? Does it stall forever? 
>>
>> Yes, it will block until detached or until a TCP
>> timeout or error closes the connection.
>>
>> The TCP timeout can take several minutes.
> 
> What I don't really understand is that how is it possible that
> a packet from TCP communication is lost? TCP resends the lost
> packets automatically. In my case I run both the usbip server
> and client on the same machine using the host name "localhost".
> So I assume that there might be a protocol handshake problem
> here.

Agreed, it doesn't seem like a TCP error is 
causing the hang in this case.

	Max

-- 
Max Vozeler - Open Source Consulting and Development, http://vozeler.com
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View attachment "0001-vhci-give-back-URBs-from-in-flight-unlink-requests.patch" of type "text/x-patch" (1933 bytes)