On Tue, 19 Mar 2013, Stephen Warren wrote: > Yes, sysrq seems to work over the serial console:-) > > > * Will now restart > > > > *** break sent *** > > [ 180.765213] SysRq : Show Blocked State > > [ 180.768963] task PC stack pid father > > [ 180.774182] khubd D c0517678 0 21 2 0x00000000 > > [ 180.780559] [<c0517678>] (__schedule+0x348/0x6dc) from [<c02ebc90>] (usb_kill_urb+0x88/0xd4) > > [ 180.788984] [<c02ebc90>] (usb_kill_urb+0x88/0xd4) from [<c02ecb70>] (usb_start_wait_urb+0xa4/0x13c) > > [ 180.798012] [<c02ecb70>] (usb_start_wait_urb+0xa4/0x13c) from [<c02ecd98>] (usb_control_msg+0x98/0xcc) > > [ 180.807301] [<c02ecd98>] (usb_control_msg+0x98/0xcc) from [<c02e4394>] (hub_port_init+0x5e0/0x9d0) > > [ 180.816242] [<c02e4394>] (hub_port_init+0x5e0/0x9d0) from [<c02e6640>] (hub_port_connect_change+0x1f4/0x970) > > [ 180.826050] [<c02e6640>] (hub_port_connect_change+0x1f4/0x970) from [<c02e70fc>] (hub_events+0x340/0x8c4) > > [ 180.835598] [<c02e70fc>] (hub_events+0x340/0x8c4) from [<c02e76a8>] (hub_thread+0x28/0x1b8) > > [ 180.843941] [<c02e76a8>] (hub_thread+0x28/0x1b8) from [<c0041268>] (kthread+0xa4/0xb0) > I assume you only want the back-traces, not the reset of the sysrq spew? Yes. It looks like khubd is your problem. > BTW, I have also occasionally noticed some either hung task or RCU spew > related to usb_kill_urb at other times (i.e. when not rebooting), IIRC > (which I may not; I may be remembering what happens if I just leave the > reboot hung for a few minutes, as shown below): > > > [ 240.670335] INFO: task khubd:21 blocked for more than 120 seconds. > > [ 240.676516] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > > [ 240.684336] khubd D c0517678 0 21 2 0x00000000 Right. It's another symptom of the same thing. This problem occurs well before shutdown -- something is causing khubd to hang and that messes up everything else. A dmesg log with CONFIG_USB_DEBUG enabled would be helpful. We ought to be able to tell where khubd is getting stuck. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
