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X-Received-From: 2a00:1450:4864:20::343 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Peter,Yuval On 3/24/20 1:05 PM, Peter Maydell wrote: > On Tue, 24 Mar 2020 at 10:54, Yuval Shaia wrote: >> To protect from the case that users of the protected_qlist are still >> using the qlist let's lock before detsroying it. >> >> Reported-by: Coverity (CID 1421951) >> Signed-off-by: Yuval Shaia >> --- >> hw/rdma/rdma_utils.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/hw/rdma/rdma_utils.c b/hw/rdma/rdma_utils.c >> index 73f279104c..55779cbef6 100644 >> --- a/hw/rdma/rdma_utils.c >> +++ b/hw/rdma/rdma_utils.c >> @@ -63,6 +63,7 @@ void rdma_protected_qlist_init(RdmaProtectedQList *list) >> void rdma_protected_qlist_destroy(RdmaProtectedQList *list) >> { >> if (list->list) { >> + qemu_mutex_lock(&list->lock); >> qlist_destroy_obj(QOBJECT(list->list)); >> qemu_mutex_destroy(&list->lock); >> list->list = NULL; > Looking at the code a bit more closely, I don't think that taking > the lock here helps. If there really could be another thread > that might be calling eg rdma_protected_qlist_append_int64() > at the same time that we're calling rdma_protected_qlist_destroy() > then it's just as likely that the code calling destroy could > finish just before the append starts: in that case the append > will crash because the list has been freed and the mutex destroyed. > > So I think we require that the user of a protected-qlist > ensures that there are no more users of it before it is > destroyed (which is fairly normal semantics), and the code > as it stands is correct (ie coverity false-positive). I agree is a false positive for our case. "rdma_protected_qlist_destroy" is called by "mad_fini" which in turn is called by "rdma_backend_fini" *after* the VM shutdown, at this point there is no active lock user. Thanks, Marcel > thanks > -- PMM