From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH for-4.5 v3] Xen and tools: Fix listing of vcpus when domains lacking any vcpus exist Date: Wed, 22 Oct 2014 12:27:31 +0100 Message-ID: <1413977251.19198.10.camel@citrix.com> References: <1413910014-4249-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1413910014-4249-1-git-send-email-andrew.cooper3@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andrew Cooper Cc: Keir Fraser , Ian Jackson , Xen-devel , Euan Harris , Jan Beulich , Wei Liu List-Id: xen-devel@lists.xenproject.org On Tue, 2014-10-21 at 17:46 +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 in Xen. getdomaininfo() has no way of expressing > "this domain has no vcpus". Previously, info->max_vcpu_id would be returned > uninitialised in such a case. > > Unfortunately, setting it to 0 as a default is not appropriate. A max_vcpu_id > of 0 and nr_online_cpus of 0 is the valid state for a single vcpu domain which > is in the process of being destroyed. > > As all components are required to add 1 to max_vcpu_id to get the number of > vcpus, an id of ~0U is not valid to be used. Explicitly define this as an > invalid max vcpu value, and use it to express "no vcpus" in getdomaininfo() > > In libxl, the issue is seen as libxl_list_vcpu() attempts to use the > uninitialised domaininfo.max_vcpu_id for memory allocation. > > Check domaininfo.max_vcpu_id against the new sentinel value > XEN_INVALID_MAX_VCPU_ID, 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 > Signed-off-by: Andrew Cooper > Acked-by: Jan Beulich > CC: Keir Fraser Tools-side: Acked-by: Ian Campbell (libxl_list_vcpu has some rather icky unconventional error handling. sigh, not your problem here though) Ian.