Re: 1.2.0 segfault on Centos 6

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On 02/04/2014 05:23 PM, Jiri Denemark wrote:
> On Tue, Feb 04, 2014 at 17:02:41 +0100, Franky Van Liedekerke wrote:
>> Hi,
>>
>> using libvirt 1.2.0 on a up-to-date Centos6.5 machine leads to 
>> occasional segmentation faults (see below).
>> Sometimes it runs for 5 minutes, sometimes for an hour, but after that 
>> the result is always the same: segfault after some weird qom-list, that 
>> apparently the qemu version on centos doesn't know. Has 1.2.1 a known 
>> fix for this?
> 
> I believe the following patch should fix the crash. I'll do some testing
> tomorrow and send it as a proper patch afterwards:
> 
> diff --git i/src/qemu/qemu_monitor.c w/src/qemu/qemu_monitor.c
> index a968901..cdd817f 100644
> --- i/src/qemu/qemu_monitor.c
> +++ w/src/qemu/qemu_monitor.c
> @@ -1019,7 +1019,9 @@ qemuMonitorFindBalloonObjectPath(qemuMonitorPtr mon,
>                                   virDomainObjPtr vm,
>                                   const char *curpath)
>  {
> -    size_t i, j, npaths = 0, nprops = 0;
> +    size_t i, j;
> +    int npaths = 0;
> +    int nprops = 0;

Reading into what the contention of the issue is, then these are perhaps
all that's needed since the conflict is I assume the difference in size
between 'int' and 'size_t'. Perhaps something Eric Blake understands
best. My simple testing shows while difference in size (4 bytes vs. 8
bytes), the compiler seems to have done the right thing on the return
value (eg, assigning 'size_t' value to a function returning int of -1).

I know when I implemented this

 http://www.redhat.com/archives/libvir-list/2013-July/msg00770.html

that I had tested without qom-list available.

Curious to know if the issue was seen in a provided or built libvirt.
It should be very simple to create a small C program that exhibits the
issue - just have a variable of size_t initialized to 0 that gets set by
a function that returns int, then print the result.


>      int ret = 0;
>      char *nextpath = NULL;
>      qemuMonitorJSONListPathPtr *paths = NULL;
> @@ -1045,6 +1047,8 @@ qemuMonitorFindBalloonObjectPath(qemuMonitorPtr mon,
>      VIR_DEBUG("Searching for Balloon Object Path starting at %s", curpath);
>  
>      npaths = qemuMonitorJSONGetObjectListPaths(mon, curpath, &paths);
> +    if (npaths < 0)
> +        return -1;
>  
>      for (i = 0; i < npaths && ret == 0; i++) {

We wouldn't enter the loop in the 0 < -1 case, but would if 0 < 0x0000ffff

>  
> @@ -1061,6 +1065,11 @@ qemuMonitorFindBalloonObjectPath(qemuMonitorPtr mon,
>               * then this version of qemu/kvm does not support the feature.
>               */
>              nprops = qemuMonitorJSONGetObjectListPaths(mon, nextpath, &bprops);
> +            if (nprops < 0) {
> +                ret = -1;
> +                goto cleanup;
> +            }
> +
>              for (j = 0; j < nprops; j++) {

same here.

>                  if (STREQ(bprops[j]->name, "guest-stats-polling-interval")) {
>                      VIR_DEBUG("Found Balloon Object Path %s", nextpath);
> 
> --
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> 

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