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CVS commit: src/sys/arch/xen/xenbus

Module Name:    src
Committed By:   royger
Date:           Wed Nov 28 16:26:59 UTC 2012

Modified Files:
        src/sys/arch/xen/xenbus: xenbus_xs.c

Log Message:
xen: prevent adding duplicate xenwatches

When a xenstore watch triggers, the event is processed on process_msg
and if a valid handle it's found the handler is queued for execution
on the pending xen watches queue (watch_events).

This may present a problem if we trigger a xenwatch several times and
then disconnect the device. If several xenwatch events are added to
the watch_events queue and the device is disconnected afterwards, the
first processed xenwatch event will disconnect the device, remove the
watch and free all resources. This triggers a panic if there are
pending xenwatch events for that device already queued in the local
queue of the function xenwatch_thread, since when the next watch that
has the same handler tries to execute we get a panic due to the fact
that the device is already disconnected and all resources had been

xenbus_watch: 0xffffa0000b7cd1d0
xbw_callback: 0xffffffff80755dd4
otherend_changed: backend/vif/1/0
backend/vif/1/0/state 6
backend/vif/1/0 -> Closed
backend/vif/1/0 -> backend_device, b_detach: 0xffffffff8075a2bf
xenbus_watch: 0xffffa0000b7cd1d0
xbw_callback: 0xfc5ec02183e547a8
fatal protection fault in supervisor mode
trap type 4 code 0 rip ffffffff80756596 cs e030 rflags 10246 cr2
7f7ff7b4c020 ilevel 0 rsp ffffa000e6d82c50
curlwp 0xffffa0000a72d580 pid 0 lid 36 lowest kstack
kernel: protection fault trap, code=0
Stopped in pid 0.36 (system) at netbsd:xenwatch_thread+0xc7:    call
xenwatch_thread() at netbsd:xenwatch_thread+0xc7
ds          f
es          5987
fs          2c40
gs          1460
rdi         ffffa0000b7cd1d0
rsi         ffffa0000a5477f0
rbp         ffffa000e6d82c70
rbx         ffffa0000b7c14c0
rdx         2
rcx         f
rax         ffffa0000b7cd1d0
r8          78
r9          ffffffef
r10         deadbeef
r11         1
r12         ffffa000e6d82c50
r13         ffffa0000a72d580
r14         ffffa0000a72d580
r15         0
rip         ffffffff80756596    xenwatch_thread+0xc7
cs          e030
rflags      10246
rsp         ffffa000e6d82c50
ss          e02b
netbsd:xenwatch_thread+0xc7:    call    *10(%rax)

To generate a diff of this commit:
cvs rdiff -u -r1.22 -r1.23 src/sys/arch/xen/xenbus/xenbus_xs.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.

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