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Re: [libvirt] [PATCH 2/2] qemu: avoid corruption of domain hashtable and misuse of freed domains



On 03/03/2011 12:47 PM, Laine Stump wrote:
> This was also found while investigating
> 
>    https://bugzilla.redhat.com/show_bug.cgi?id=670848
> 
> An EOF on a domain's monitor socket results in an event being queued
> to handle the EOF. The handler calls qemuProcessHandleMonitorEOF. If
> it is a transient domain, this leads to a call to
> virDomainRemoveInactive, which removes the domain from the driver's
> hashtable and unref's it. Nowhere in this code is the qemu driver lock
> acquired.
> 
> However, all modifications to the driver's domain hashtable *must* be
> done while holding the driver lock, otherwise the hashtable can become
> corrupt, and (even more likely) another thread could call a different
> hashtable function and acquire a pointer to the domain that is in the
> process of being destroyed.
> 
> To prevent such a disaster, qemuProcessHandleMonitorEOF must get the
> qemu driver lock *before* it gets the DomainObj's lock, and hold it
> until it is finished with the DomainObj. This guarantees that nobody
> else modifies the hashtable at the same time, and that anyone who had
> already gotten the DomainObj from the hashtable prior to this call has
> finished with it before we remove/destroy it.
> ---
>  src/qemu/qemu_process.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)

Makes sense to me, given src/qemu/THREADS.txt, but you may want to wait
for danpb's ACK as well.

-- 
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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