Re: [libvirt] [PATCH] virObject: Error on suspicious ref and unref

https://bugzilla.redhat.com/show_bug.cgi?id=1033061 Since our transformation into virObject is not complete and we must do ref and unref ourselves there's a chance that we will get it wrong. That is, while one thread is doing unref and subsequent dispose another thread may come and do the ref & unref on stale pointer. This results in dispose being called twice (and possibly simultaneously). These kind of errors are hard to catch so we should at least throw an error into logs if such situation occurs. In fact, I've seen a stack trace showing this error had happen (obj = 0x7f4968018260):

diff --git a/src/util/viratomic.h b/src/util/viratomic.h index 4d7f7e5..877900e 100644 --- a/src/util/viratomic.h +++ b/src/util/viratomic.h @@ -68,6 +68,18 @@ VIR_STATIC int virAtomicIntInc(volatile int *atomic) ATTRIBUTE_NONNULL(1); /** + * virAtomicIntDec: + * Decrements the value of atomic by 1. + * + * Think of this operation as an atomic version of + * { *atomic -= 1; return *atomic == 0; }

+ * + * This call acts as a full compiler and hardware memory barrier. + */ +VIR_STATIC int virAtomicIntDec(volatile int *atomic) + ATTRIBUTE_NONNULL(1); + +/**