On Mon, Mar 23, 2015 at 11:25 AM, Tamas K Lengyel <tkleng...@sec.in.tum.de> wrote:
> On Mon, Mar 23, 2015 at 6:59 PM, Andres Lagar Cavilla < > and...@lagarcavilla.org> wrote: > >> On Mon, Mar 23, 2015 at 9:10 AM, Tamas K Lengyel <tkleng...@sec.in.tum.de >> > wrote: >> >>> Hello everyone, >>> I'm trying to chase down a bug that reproducibly crashes Xen (tested >>> with 4.4.1). The problem is somewhere within the mem-sharing subsystem and >>> how that interacts with domains that are being actively saved. In my setup >>> I use the xl toolstack to rapidly create clones of HVM domains by piping >>> "xl save -c" into xl restore with a modified domain config which updates >>> the name/disk/vif. However, during such an operation Xen crashes with the >>> following log if there are already active clones. >>> >>> IMHO there should be no conflict between saving the domain and >>> memsharing, as long as the domain is actually just being checkpointed "-c" >>> - it's memory should remain as is. This is however clearly not the case. >>> Any ideas? >>> >> >> Tamas, I'm not clear on the use of memsharing in this workflow. As >> described, you pipe save into restore, but the internal magic is lost on >> me. Are you fanning out to multiple restores? That would seem to be the >> case, given the need to update name/disk/vif. >> >> Anyway, I'm inferring. Instead, could you elaborate? >> >> Thanks >> Andre >> > > Hi Andre, > thanks for getting back on this issue. The script I'm using is at > https://github.com/tklengyel/drakvuf/blob/master/tools/clone.pl. The > script simply creates a FIFO pipe (mkfifo) and saves the domain into that > pipe which is immediately read by xl restore with the updated configuration > file. This mainly just to eliminate having to read the memory dump from > disk. That part of the system works as expected and multiple save/restores > running at the same time don't cause any side-effects. Once the domain has > thus been cloned, I run memshare on every page which also works as > expected. This problem only occurs when the cloning procedure runs when a > page unshare operation kicks in on a already active clone (as you see in > the log). > Sorry Tamas, I'm a bit slow here, I looked at your script -- looks allright, no mention of memsharing in there. Re-reading ... memsharing? memshare? Is this memshrtool in tools/testing? How are you running it? Certainly no xen crash should happen with user-space input. I'm just trying to understand what you're doing. The unshare code is not, uhmm, brief, so a NULL deref could happen in half a dozen places at first glance. Thanks Andres > > Tamas >
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