[Xen-devel] RE: Bug in tmem: refcount leak leaves zombie saved domains

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

OK, will take a look.

IIRC, Jan's work to fix the domain reference stuff just
before 4.0 shipped was a heavy hammer but since it seemed
to work, I didn't want to mess with it so close to release...
really there's only a need to take a reference once on
first use and release it at shutdown, rather than
take/release frequently.  IIRC, I had used a macro that
took references when they weren't really needed and
Jan placed the matching macros that did the release.

Dan

> -----Original Message-----
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> Sent: Thursday, June 10, 2010 3:47 AM
> To: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: Dan Magenheimer
> Subject: Bug in tmem: refcount leak leaves zombie saved domains
> 
> Dan,
> 
> Just doing some save/restore testing on xen-unstable tip, I noticed
> that:
> # xm create ./pv_config
> # xm save PV1
> 
> Would leave the saved guest as a zombie in the DOMDYING_dead state with
> no
> pages, yet with refcnt=1. This happens absolutely consistently. Just as
> consistently, it does not happen when I boot Xen with no-tmem. My
> conclusion
> is that tmem is leaking a domain reference count during domain save.
> This
> doesn't happen if I merely "xm create ...; xm destroy ...".
> 
> My pv_config file contains nothing exciting:
> kernel = "/nfs/keir/xen/xen64.hg/dist/install/boot/vmlinuz-2.6.18.8-
> xenU"
> memory = 750
> name = "PV1"
> vcpus = 2
> vif = [ 'mac=00:1a:00:00:01:01' ]
> disk = [ 'phy:/dev/VG/Suse10.1_64_1,sda1,w' ]
> root = "/dev/sda1 ro xencons=tty"
> extra = ""
> tsc_native = 1
> on_poweroff = 'destroy'
> on_reboot   = 'restart'
> on_crash    = 'preserve'
> 
> The dom{0,U} kernels are tip of linux-2.6.18-xen, default -xen{0,U}
> configs.
> 
>  -- Keir
> 
> 

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