[libvirt] [PATCH] Fix potential events deadlock when unref'ing virConnectPtr
Eric Blake
eblake at redhat.com
Mon May 21 15:07:50 UTC 2012
On 05/21/2012 05:17 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange" <berrange at redhat.com>
>
> When the last reference to a virConnectPtr is released by
> libvirtd, it was possible for a deadlock to occur in the
> virDomainEventState functions. The virDomainEventStatePtr
> holds a reference on virConnectPtr for each registered
> callback. When removing a callback, the virUnrefConnect
> function is run. If this causes the last reference on the
> virConnectPtr to be released, then virReleaseConnect can
> be run, which in turns calls qemudClose. This function has
> a call to virDomainEventStateDeregisterConn which is intended
> to remove all callbacks associated with the virConnectPtr
> instance.
>
> Since each callback associated with a virConnectPtr holds a
> reference on virConnectPtr, it is impossible for the qemudClose
> method to be invoked while any callbacks are still registered.
> Thus the call to virDomainEventStateDeregisterConn must in fact
> be a no-op. Thus it is possible to just remove all trace of
> virDomainEventStateDeregisterConn and avoid the deadlock.
>
> * src/conf/domain_event.c, src/conf/domain_event.h,
> src/libvirt_private.syms: Delete virDomainEventStateDeregisterConn
> * src/libxl/libxl_driver.c, src/lxc/lxc_driver.c,
> src/qemu/qemu_driver.c, src/uml/uml_driver.c: Remove
> calls to virDomainEventStateDeregisterConn
> ---
> src/conf/domain_event.c | 61 ----------------------------------------------
> src/conf/domain_event.h | 4 ---
> src/libvirt_private.syms | 1 -
> src/libxl/libxl_driver.c | 4 ---
> src/lxc/lxc_driver.c | 2 --
> src/qemu/qemu_driver.c | 2 --
> src/uml/uml_driver.c | 2 --
> 7 files changed, 76 deletions(-)
Always fun to fix bugs by deletion.
ACK.
--
Eric Blake eblake at redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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