Re: bug in usbback

[Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>]

Hi James,

Reconfiguring/Resconfigured states are used to notify the hotplug
event, as follows.


usb device    usbback                     usbfront
---------     -------                     --------

             Connected                    Connected
                  |                           |
---plug&probe--->|                           |
                  |                           |
            Reconfiguring-------------------->|
                  |                           |
                  | <---------------------Reconfiguring
                  |                           |
                  |                           |
          usbback_do_hotplug()                |
                  |                           |
                  |                           |
             Reconfigured-------------------->|
                  |                           |
                  |                           |
                  |                  usbfront_do_hotplug()
                  |                           |
                  |                           |
                  |<----------------------Connected
                  |                           |
              Connected                       |
                  |                           |


You mean:
- Your version of usbfront NOT respond to Reconfiguring state.
   It's not bug of original usbfront.
- When usbback is in Reconfiguring state and usbfront NOT respond to
   that, rebooting domU causes the BUG.

Is my understanding right?

Regards,
Noboru

James Harper wrote:
> I think there is a bug in pvusb when the DomU does not respond to the
> XenbusStateReconfiguring state change and is then rebooted. This caused
> the following Dom0 (after a long freeze):
> 
> BUG: soft lockup detected on CPU#0!
> 
> Call Trace:
>  <IRQ> [<ffffffff802a938c>] softlockup_tick+0xe1/0xef
>  [<ffffffff80268f82>] timer_interrupt+0x408/0x466
>  [<ffffffff8020fb41>] handle_IRQ_event+0x4d/0x95
>  [<ffffffff802a9870>] __do_IRQ+0xb4/0x127
>  [<ffffffff8026729c>] do_IRQ+0x44/0x4d
>  [<ffffffff80375f6b>] evtchn_do_upcall+0x1b3/0x26e
>  [<ffffffff8025c8d2>] do_hypervisor_callback+0x1e/0x2c
>  <EOI> [<ffffffff88355b7e>] :usbbk:usbbk_schedule+0x1e0/0xa3f
>  [<ffffffff8029482f>] autoremove_wake_function+0x0/0x2e
>  [<ffffffff802947ba>] keventd_create_kthread+0x0/0x62
>  [<ffffffff8835599e>] :usbbk:usbbk_schedule+0x0/0xa3f
>  [<ffffffff802947ba>] keventd_create_kthread+0x0/0x62
>  [<ffffffff802325e4>] kthread+0xd4/0x108
>  [<ffffffff8025cb24>] child_rip+0xa/0x12
>  [<ffffffff802947ba>] keventd_create_kthread+0x0/0x62
>  [<ffffffff8025c827>] error_exit+0x0/0x71
>  [<ffffffff80232510>] kthread+0x0/0x108
>  [<ffffffff8025cb1a>] child_rip+0x0/0x12
>  
> FYI, I am trying to get pvusb working under GPLPV and I had never seen
> the Reconfiguring/Reconfigured states before and so I wasn't doing
> anything with them...
> 
> James
> 
> 
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