[libvirt] [PATCH v3] qemu: fix libvirtd crash when querying halted cpus info

[Peter Krempa]

On Tue, Nov 15, 2016 at 17:09:33 +0300, Maxim Nestratov wrote:
> It was introduced by commit 7a51d9ebb, which started to use
> monitor commands without job acquiring, which is unsafe and leads
> to simultaneous access to vm->mon structure by different threads.
> 
> Crash backtrace is the following (shortened):
> 
> Program received signal SIGSEGV, Segmentation fault.
> qemuMonitorSend (mon=mon at entry=0x7f4ef4000d20, msg=msg at entry=0x7f4f18e78640) at qemu/qemu_monitor.c:1011
> 1011        while (!mon->msg->finished) {
> 
> 0  qemuMonitorSend () at qemu/qemu_monitor.c:1011
> 1  0x00007f691abdc720 in qemuMonitorJSONCommandWithFd () at qemu/qemu_monitor_json.c:298
> 2  0x00007f691abde64a in qemuMonitorJSONCommand at qemu/qemu_monitor_json.c:328
> 3  qemuMonitorJSONQueryCPUs at qemu/qemu_monitor_json.c:1408
> 4  0x00007f691abcaebd in qemuMonitorGetCPUInfo g at entry=false) at qemu/qemu_monitor.c:1931
> 5  0x00007f691ab96863 in qemuDomainRefreshVcpuHalted at qemu/qemu_domain.c:6309
> 6  0x00007f691ac0af99 in qemuDomainGetStatsVcpu at qemu/qemu_driver.c:18945
> 7  0x00007f691abef921 in qemuDomainGetStats  at qemu/qemu_driver.c:19469
> 8  qemuConnectGetAllDomainStats at qemu/qemu_driver.c:19559
> 9  0x00007f693382e806 in virConnectGetAllDomainStats at libvirt-domain.c:11546
> 10 0x00007f6934470c40 in remoteDispatchConnectGetAllDomainStats at remote.c:6267
> 
> (gdb) p mon->msg
> $1 = (qemuMonitorMessagePtr) 0x0
> 
> This change fixes it by calling qemuDomainRefreshVcpuHalted only when job is acquired.
> 
> Signed-off-by: Maxim Nestratov <mnestratov at virtuozzo.com>
> ---
> v1-v2: don't output halted cpu info if it wasn't rathered
> v2-v3: syntax-check recommendation 
> 
>  src/qemu/qemu_driver.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)

ACK
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