From 5f5c515bbdcb7ce8db12544033fad393eb2a1c41 Mon Sep 17 00:00:00 2001 From: "Daniel P. Berrange" Date: Fri, 1 Sep 2017 13:47:04 +0100 Subject: [PATCH] event: ignore attempts to replace the event loop impl Although not previously explicitly documented, the expectation for the libvirt event loop is that an implementation is registered early in application startup, before calling any libvirt APIs and then run forever after. Replacing a previously registered event loop is not safe & subject to races even if virConnectClose has been called on open handles, due to delayed deregistration of callbacks during conenction close. Reviewed-by: Andrea Bolognani Signed-off-by: Daniel P. Berrange --- src/util/virevent.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/src/util/virevent.c b/src/util/virevent.c index e0fd35e416..51d8714df4 100644 --- a/src/util/virevent.c +++ b/src/util/virevent.c @@ -220,6 +220,13 @@ virEventRemoveTimeout(int timer) * existing event loop implementation, then the * virEventRegisterDefaultImpl() method can be used to setup * the generic libvirt implementation. + * + * Once registered, the event loop implementation cannot be + * changed, and must be run continuously. Note that callbacks + * may remain registered for a short time even after calling + * virConnectClose on all open connections, so it is not safe + * to stop running the event loop immediately after closing + * the connection. */ void virEventRegisterImpl(virEventAddHandleFunc addHandle, virEventUpdateHandleFunc updateHandle, @@ -233,6 +240,12 @@ void virEventRegisterImpl(virEventAddHandleFunc addHandle, addHandle, updateHandle, removeHandle, addTimeout, updateTimeout, removeTimeout); + if (addHandleImpl || updateHandleImpl || removeHandleImpl || + addTimeoutImpl || updateTimeoutImpl || removeHandleImpl) { + VIR_WARN("Ignoring attempt to replace registered event loop"); + return; + } + addHandleImpl = addHandle; updateHandleImpl = updateHandle; removeHandleImpl = removeHandle; -- GitLab