On 03/19/2013 02:07 PM, Alan Stern wrote: > 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. Hmmm. Enabling CONFIG_USB_DEBUG appears to mask the problem. I assume this is some kind of timing/race condition, unless there's some code with required side-effects hiding under ifdef CONFIG_USB_DEBUG somehow? -- 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
