On 05/03/2018 08:34 AM, Erik Skultety wrote:
On Tue, Apr 24, 2018 at 08:28:08AM -0400, John Ferlan wrote:
Since the @dconn reference via args->conn will be used via a thread or callback, let's make sure memory associated with it isn't free'd unexpectedly before we use it. The Unref will be done when the object is Dispose'd.
Signed-off-by: John Ferlan <jferlan@redhat.com> --- src/libxl/libxl_migration.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/src/libxl/libxl_migration.c b/src/libxl/libxl_migration.c index 7fe352306c..d37a4a687a 100644 --- a/src/libxl/libxl_migration.c +++ b/src/libxl/libxl_migration.c @@ -239,6 +239,7 @@ libxlMigrationDstArgsDispose(void *obj)
libxlMigrationCookieFree(args->migcookie); VIR_FREE(args->socks); + virObjectUnref(args->conn); virObjectUnref(args->vm); }
@@ -608,7 +609,7 @@ libxlDomainMigrationDstPrepareTunnel3(virConnectPtr dconn, if (!(args = virObjectNew(libxlMigrationDstArgsClass))) goto error;
- args->conn = dconn; + args->conn = virObjectRef(dconn); args->vm = virObjectRef(vm); args->flags = flags; args->migcookie = mig; @@ -763,7 +764,7 @@ libxlDomainMigrationDstPrepare(virConnectPtr dconn, if (!(args = virObjectNew(libxlMigrationDstArgsClass))) goto error;
- args->conn = dconn; + args->conn = virObjectRef(dconn); args->vm = virObjectRef(vm); args->flags = flags; args->socks = socks;
Do you actually have a use case, where the conn object would be destroyed before the migration finishes in a way that this could cause a SIGSEGV?
Nope - just fear and protection any such possibility. We're saving a pointer to some object in an object and possibly dereferencing it at some point in time in the future during libxlDoMigrateDstReceive. Other places where we do similar things w/ conn we also add a Ref to it. And yes, patch 4 and 5 could be separate, perhaps more so this patch than patch 4 because of how patch 6 changes @vm refcnt. It shouldn't be possible to have a failure condition for either Ref, but those are always "famous last words" and really difficult to diagnose after the fact. It doesn't hurt to Ref and then Unref AFAIK. John