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SubjectRe: USB device cannot be reconnected and khubd "blocked for more than 120 seconds"
On Sat, Jan 12, 2013 at 6:37 PM, Alan Stern <> wrote:
> On Sat, 12 Jan 2013, Alex Riesen wrote:
>> On Fri, Jan 11, 2013 at 10:04 PM, Alex Riesen <> wrote:
>> >
>> > the USB stick (an Cruzer Titanium 2GB) was not recognized at any of
>> > the USB ports of this system (an System76 lemu4 laptop, XHCI device)
>> > after it was removed. [...]
> To make testing simpler, use only the USB-2 ports. The xHCI driver is
> not as mature as the EHCI driver.

I used the USB2 port, but enabled the debugging for xHCI too, just because
it is not as mature as you say, but in the same machine. And there are some
traces from it, even though I didn't touch the USB3 ports.
Might be unrelated, but just in case...

>> > The kernel is v3.8-rc3. I never had this problem in 3.7. I could almost

For the record, I just retested: the problem persists with 3.7.1.

>> > reproduce the problem later in a simplified setup (init=/bin/bash) on
>> > USB3 ports by inserting and removing the stick quickly. Almost - because
>> > the USB3 ports recovered after some time, while the USB2 port never
>> > experienced the problem.
> For testing, use a kernel with CONFIG_USB_DEBUG and CONFIG_PRINTK_TIME
> enabled. Do the following:
> After a normal boot, run "dmesg -C" to clear the log buffer.
> Then plug in the stick. After a couple of seconds, type Alt-SysRq-W.
> Then unplug the stick. After a couple of seconds, type Alt-SysRq-W
> again.
> Then collect the output from dmesg and post it.

Attached. A remount in the middle is me remounting an SATA device to
save dmesg output in case the system crashes hard.
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