[Xen-devel] xl dev-detach hangs with missing frontends

[Olaf Hering <olaf@xxxxxxxxx>]

How should libxl__initiate_device_generic_remove deal with devices which
have no frontend driver? Right now it moves "state" from either
XenbusStateInitialising or XenbusStateInitWait to XenbusStateClosing.
Then it expects the backend to move "state" to XenbusStateClosed. This
will never happen, at least for netback and scsiback. The result is a 10
second delay.


# xl -vvvv network-detach $domU $mac
2016-02-11 11:33:19 CET [20318] libxl: debug: 
libxl.c:4614:libxl_device_nic_remove: ao 0x19b3870: create: how=(nil) 
callback=(nil) poller=0x19b0200
2016-02-11 11:33:19 CET [20318] libxl: debug: 
libxl_event.c:636:libxl__ev_xswatch_register: watch w=0x19b2c40 
wpath=/local/domain/0/backend/vif/10/1/state token=3/0: register slotnum=3
2016-02-11 11:33:19 CET [20318] libxl: debug: 
libxl.c:4614:libxl_device_nic_remove: ao 0x19b3870: inprogress: 
poller=0x19b0200, flags=i
2016-02-11 11:33:19 CET [20318] libxl: debug: 
libxl_event.c:573:watchfd_callback: watch w=0x19b2c40 
wpath=/local/domain/0/backend/vif/10/1/state token=3/0: event 
epath=/local/domain/0/backend/vif/10/1/state
2016-02-11 11:33:19 CET [20318] libxl: debug: 
libxl_event.c:878:devstate_callback: backend 
/local/domain/0/backend/vif/10/1/state wanted state 6 still waiting state 5
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_aoutils.c:88:xswait_timeout_callback: backend 
/local/domain/0/backend/vif/10/1/state (hoping for state change to 6): xswait 
timeout (path=/local/domain/0/backend/vif/10/1/state)
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:673:libxl__ev_xswatch_deregister: watch w=0x19b2c40 
wpath=/local/domain/0/backend/vif/10/1/state token=3/0: deregister slotnum=3
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:862:devstate_callback: backend 
/local/domain/0/backend/vif/10/1/state wanted state 6  timed out
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:686:libxl__ev_xswatch_deregister: watch w=0x19b2c40: deregister 
unregistered
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_device.c:939:device_backend_callback: calling device_backend_cleanup
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:686:libxl__ev_xswatch_deregister: watch w=0x19b2c40: deregister 
unregistered
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_device.c:945:device_backend_callback: Timeout reached, initiating forced 
remove
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:636:libxl__ev_xswatch_register: watch w=0x19b2c40 
wpath=/local/domain/0/backend/vif/10/1/state token=3/1: register slotnum=3
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:573:watchfd_callback: watch w=0x19b2c40 
wpath=/local/domain/0/backend/vif/10/1/state token=3/1: event 
epath=/local/domain/0/backend/vif/10/1/state
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:874:devstate_callback: backend 
/local/domain/0/backend/vif/10/1/state wanted state 6 ok
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:673:libxl__ev_xswatch_deregister: watch w=0x19b2c40 
wpath=/local/domain/0/backend/vif/10/1/state token=3/1: deregister slotnum=3
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_device.c:939:device_backend_callback: calling device_backend_cleanup
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:686:libxl__ev_xswatch_deregister: watch w=0x19b2c40: deregister 
unregistered
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_device.c:1036:device_hotplug: calling hotplug script: 
/opt/xen/staging-wip/etc/xen/scripts/vif-bridge offline
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_aoutils.c:593:libxl__async_exec_start: forking to execute: 
/opt/xen/staging-wip/etc/xen/scripts/vif-bridge offline
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:542:watchfd_callback: watch 
epath=/local/domain/0/backend/vif/10/1/state token=3/1: empty slot
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:686:libxl__ev_xswatch_deregister: watch w=0x19b2d40: deregister 
unregistered
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_device.c:1023:device_hotplug: No hotplug script to execute
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:686:libxl__ev_xswatch_deregister: watch w=0x19b2d40: deregister 
unregistered
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:1869:libxl__ao_complete: ao 0x19b3870: complete, rc=0
2016-02-11 11:33:29 CET [20318] libxl: debug: 
libxl_event.c:1838:libxl__ao__destroy: ao 0x19b3870: destroy
2016-02-11 11:33:29 CET [20318] xencall:buffer: debug: total allocations:22 
total releases:22
2016-02-11 11:33:29 CET [20318] xencall:buffer: debug: current allocations:0 
maximum allocations:2
2016-02-11 11:33:29 CET [20318] xencall:buffer: debug: cache current size:2
2016-02-11 11:33:29 CET [20318] xencall:buffer: debug: cache hits:14 misses:2 
toobig:6
# echo $?
0

At least ${dev}-detach reports no error in this case.

Olaf

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