Re: sysfs interface to force power off

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Lukas, Hans]

On Fri, Nov 04, 2022 at 07:08:34PM -0400, James Puthukattukaran wrote:
> Looking to solve a problem where we have nvme drives that are hung
> in the field and we are not sure of the root cause but the working
> theory is that the controller is "bad" and not responding properly
> to commands. The nvme driver times out on outstanding IO requests
> and as part of recovery, attempts to reset the controller and
> reinitialize the device. The reset controller also hangs like here
> --   
> 
> ernel:info: [10419813.132341] Workqueue: nvme-reset-wq nvme_reset_work [nvme]
> kernel:warning: [10419813.132342] Call Trace:
> kernel:warning: [10419813.132345]  __schedule+0x2bc/0x89b
> kernel:warning: [10419813.132348]  schedule+0x36/0x7c
> kernel:warning: [10419813.132351]  blk_mq_freeze_queue_wait+0x4b/0xaa
> kernel:warning: [10419813.132353]  ? remove_wait_queue+0x60/0x60
> kernel:warning: [10419813.132359]  nvme_wait_freeze+0x33/0x50 [nvme_core]
> kernel:warning: [10419813.132362]  nvme_reset_work+0x802/0xd84 [nvme]
> kernel:warning: [10419813.132364]  ? __switch_to_asm+0x40/0x62
> kernel:warning: [10419813.132365]  ? __switch_to_asm+0x34/0x62
> kernel:warning: [10419813.132367]  ? __switch_to+0x9b/0x505
> kernel:warning: [10419813.132368]  ? __switch_to_asm+0x40/0x62
> kernel:warning: [10419813.132370]  ? __switch_to_asm+0x40/0x62
> kernel:warning: [10419813.132372]  process_one_work+0x169/0x399
> kernel:warning: [10419813.132374]  worker_thread+0x4d/0x3e5
> kernel:warning: [10419813.132377]  kthread+0x105/0x138
> kernel:warning: [10419813.132379]  ? rescuer_thread+0x380/0x375
> kernel:warning: [10419813.132380]  ? kthread_bind+0x20/0x15
> kernel:warning: [10419813.132382]  ret_from_fork+0x24/0x49
> ...
> 
> So, I tried to hot power off the device via
> "echo 0 > /sys/bus/pci/slots/X/power" -- the thread also hangs
> waiting for the nvme reset thread to finish (like so) -- 

Looks like this "power" sysfs file could use some documentation.  I
couldn't find anything in Documentation/ABI/testing/ that seems to
cover it.

> kernel:warning: [10419813.158116]  __schedule+0x2bc/0x89b
> kernel:warning: [10419813.158119]  schedule+0x36/0x7c
> kernel:warning: [10419813.158122]  schedule_timeout+0x1f6/0x31f
> kernel:warning: [10419813.158124]  ? sched_clock_cpu+0x11/0xa5
> kernel:warning: [10419813.158126]  ? try_to_wake_up+0x59/0x505
> kernel:warning: [10419813.158130]  wait_for_completion+0x12b/0x18a
> kernel:warning: [10419813.158132]  ? wake_up_q+0x80/0x73
> kernel:warning: [10419813.158134]  flush_work+0x122/0x1a7
> kernel:warning: [10419813.158137]  ? wake_up_worker+0x30/0x2b
> kernel:warning: [10419813.158141]  nvme_remove+0x71/0x100 [nvme]
> kernel:warning: [10419813.158146]  pci_device_remove+0x3e/0xb6
> kernel:warning: [10419813.158149]  device_release_driver_internal+0x134/0x1eb
> kernel:warning: [10419813.158151]  device_release_driver+0x12/0x14
> kernel:warning: [10419813.158155]  pci_stop_bus_device+0x7c/0x96
> kernel:warning: [10419813.158158]  pci_stop_bus_device+0x39/0x96
> kernel:warning: [10419813.158164]  pci_stop_and_remove_bus_device+0x12/0x1d
> kernel:warning: [10419813.158167]  pciehp_unconfigure_device+0x7a/0x1d7
> kernel:warning: [10419813.158169]  pciehp_disable_slot+0x52/0xca
> kernel:warning: [10419813.158171]  pciehp_sysfs_disable_slot+0x67/0x112
> kernel:warning: [10419813.158174]  disable_slot+0x12/0x14
> kernel:warning: [10419813.158175]  power_write_file+0x6e/0xf8
> kernel:warning: [10419813.158179]  pci_slot_attr_store+0x24/0x2e
> kernel:warning: [10419813.158180]  sysfs_kf_write+0x3f/0x46
> kernel:warning: [10419813.158182]  kernfs_fop_write+0x124/0x1a3
> kernel:warning: [10419813.158184]  __vfs_write+0x3a/0x16d
> kernel:warning: [10419813.158187]  ? audit_filter_syscall+0x33/0xce
> kernel:warning: [10419813.158189]  vfs_write+0xb2/0x1a1
> 
> Is there a way to force power off the device instead of the
> "graceful" approach? Obviously, we don't want to reset the system
> and don't have physical access to the device.  
> 
> Would it make sense to create a "force power off" in
> /sys/bus/pci/slots/X which basically 

> a) Sets completion timeout mask (CTO) (for outstanding IO requests
>    not causing a fatal error due to CTOs; not an issue for DPCs I
>    would think)
> b) power off the slot 
> c) enable CTO mask
> d) unconfigure the device via pciehp_unconfigure_device

So I assume the existing sysfs slot "power" interface would do what
you want except that nvme_remove() hangs?

There might be some improvement to make in nvme_remove(); maybe it
doesn't correctly detect I/O errors or something.

But maybe there's *also* a case to be made for an interface like you
suggest.  Lukas, Hans, any reaction to this?

Bjorn