panic in portallocator when updating service

[allencloud]

Hi, All,

When I was updating service, panic happened in docker engine's log, like below:

time="2016-09-01T12:03:35.697250351+08:00" level=error msg="Handler for GET /v1.24/services/dy7yajeu246ztckluq367wvfo returned error: service dy7yajeu246ztckluq367wvfo not found" 
time="2016-09-01T12:03:55.532280461+08:00" level=error msg="Error updating service adnfj9n8um05: rpc error: code = 5 desc = service adnfj9n8um05 not found" 
time="2016-09-01T12:03:55.532477499+08:00" level=error msg="Handler for POST /v1.24/services/adnfj9n8um05/update returned error: rpc error: code = 5 desc = service adnfj9n8um05 not found" 
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x10 pc=0x14b2dcc]

goroutine 264 [running]:
panic(0x1a619a0, 0xc820010070)
    /usr/local/go/src/runtime/panic.go:481 +0x3e6
github.com/docker/swarmkit/manager/allocator/networkallocator.(*portAllocator).isPortsAllocated(0xc82001e278, 0xc82170b500, 0xc820811880)
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/networkallocator/portallocator.go:164 +0x4c
github.com/docker/swarmkit/manager/allocator/networkallocator.(*NetworkAllocator).IsServiceAllocated(0xc82075cd50, 0xc82170b500, 0xc82175ac20)
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/networkallocator/networkallocator.go:309 +0xeb
github.com/docker/swarmkit/manager/allocator.(*Allocator).doNetworkAlloc(0xc82075c2a0, 0x7f861aed9a38, 0xc8201835c0, 0x1b1c4c0, 0xc82175ac20)
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/network.go:318 +0x369
github.com/docker/swarmkit/manager/allocator.(*Allocator).(github.com/docker/swarmkit/manager/allocator.doNetworkAlloc)-fm(0x7f861aed9a38, 0xc8201835c0, 0x1b1c4c0, 0xc82175ac20)
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/allocator.go:117 +0x48
github.com/docker/swarmkit/manager/allocator.(*Allocator).run(0xc82075c2a0, 0x7f861aed9a38, 0xc8201835c0, 0xc82075a000, 0xc82075cc00, 0x1d44b28, 0x7, 0xc8208a1680, 0xc8208a1670)
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/allocator.go:175 +0x118
github.com/docker/swarmkit/manager/allocator.(*Allocator).Run.func2.1(0xc8208a1600, 0xc82075c2a0, 0xc8208a15e0, 0xc82075a000, 0xc82075cc00, 0x1d44b28, 0x7, 0xc8208a1680, 0xc8208a1670)
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/allocator.go:142 +0xa9
created by github.com/docker/swarmkit/manager/allocator.(*Allocator).Run.func2
    /usr/src/docker/vendor/src/github.com/docker/swarmkit/manager/allocator/allocator.go:143 +0x13c

It leads to the restart of engine. In some case, it brings severe consequence.