Re: [Xen-devel] [PATCH for-4.5 v2 2/2] tools/[lib]xl: Fix `xl vcpu-list` when domains without vcpus exist

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Oct 20, 2014 at 05:38:54PM +0100, Andrew Cooper wrote:
> On a system which looks like this:
> 
> [root@st04 ~]# xl list
> Name                                        ID   Mem VCPUs      State   
> Time(s)
> Domain-0                                     0   752     4     r-----   
> 46699.3
> (null)                                       1     0     0     --p---       
> 0.0
> (null)                                       2     0     0     --p---       
> 0.0
> (null)                                       3     0     0     --p---       
> 0.0
> badger                                      25     0     1     --p---       
> 0.0
> 
> `xl vcpu-list` failes as so:
> 
> [root@st04 ~]# xl vcpu-list
> Name                                ID  VCPU   CPU State   Time(s) CPU 
> Affinity
> Domain-0                             0     0    0   -b-   12171.0  all
> Domain-0                             0     1    1   -b-   11779.6  all
> Domain-0                             0     2    2   -b-   11599.0  all
> Domain-0                             0     3    3   r--   11007.0  all
> libxl: critical: libxl__calloc: libxl: FATAL ERROR: memory allocation failure 
> (libxl__calloc, 4294935299 x 40)
> : Cannot allocate memory
> libxl: FATAL ERROR: memory allocation failure (libxl__calloc, 4294935299 x 40)
> 
> The root cause of this is that, in the case that a domain has no vcpus,
> libxl_list_vcpu() attempts to calloc() with domaininfo.max_vcpu_id, which
> is uninitialised on the stack.
> 
> Check domaininfo.max_vcpu_id against the new sentinel value
> XEN_INVALID_MAX_VCPU_ID (introduced in the previous patch), and return early.
> This means that it is now valid for libxl_list_vcpu() to return NULL for a
> domain which lacks any vcpus.
> 
> As part of this change, remove the pointless call to libxl_get_max_cpus(),
> whose returned value is unconditionally clobbered in the for() loop.
> 
> Reported-by: Euan Harris <euan.harris@xxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> ---
> v2: s/nr_online_cpus/max_vcpu_id/g - I accidentally sent an unrefreshed patch
> ---
>  tools/libxl/libxl.c      |    8 +++++++-
>  tools/libxl/xl_cmdimpl.c |    4 +---
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index f27b581..b7a9952 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -5246,7 +5246,13 @@ libxl_vcpuinfo *libxl_list_vcpu(libxl_ctx *ctx, 
> uint32_t domid,
>          GC_FREE;
>          return NULL;
>      }
> -    *nr_cpus_out = libxl_get_max_cpus(ctx);
> +
> +    if (domaininfo.max_vcpu_id == XEN_INVALID_MAX_VCPU_ID) {
> +        *nr_cpus_out = 0;

Do you not need to set nr_vcpus_out to 0 as well?

Wei.

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