From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: [Xen-devel] [PATCH] xen-netfront: wait xenbus state change when load module manually Date: Fri, 24 Aug 2018 13:26:38 +0200 Message-ID: <830d73b5-8bbb-4d9a-a004-7aeea0b35067@suse.com> References: <20180727095608.25210-1-xiliang@redhat.com> <20180729.083040.53901922165497594.davem@davemloft.net> <60e93e09-7dc2-d2f6-379d-c1d086aa1f49@redhat.com> <83ad1e3c-5e3b-8b24-430b-13e12b59ae8b@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: netdev@vger.kernel.org, boris.ostrovsky@oracle.com, linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org To: Jiri Slaby , Xiao Liang , David Miller Return-path: In-Reply-To: <83ad1e3c-5e3b-8b24-430b-13e12b59ae8b@suse.cz> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 24/08/18 13:12, Jiri Slaby wrote: > On 07/30/2018, 10:18 AM, Xiao Liang wrote: >> On 07/29/2018 11:30 PM, David Miller wrote: >>> From: Xiao Liang >>> Date: Fri, 27 Jul 2018 17:56:08 +0800 >>> >>>> @@ -1330,6 +1331,11 @@ static struct net_device >>>> *xennet_create_dev(struct xenbus_device *dev) >>>>       netif_carrier_off(netdev); >>>>         xenbus_switch_state(dev, XenbusStateInitialising); >>>> +    wait_event(module_load_q, >>>> +               xenbus_read_driver_state(dev->otherend) != >>>> +               XenbusStateClosed && >>>> +               xenbus_read_driver_state(dev->otherend) != >>>> +               XenbusStateUnknown); >>>>       return netdev; >>>>      exit: >>> What performs the wakeups that will trigger for this sleep site? >> In my understanding, backend leaving closed/unknow state can trigger the >> wakeups. I mean to make sure both sides are ready for creating connection. > > While backporting this to 4.12, I was surprised by the commit the same > as Boris and David. > > So I assume the explanation is that wake_up_all of module_unload_q in > netback_changed wakes also all the processes waiting on module_load_q? > If so, what makes sure that module_unload_q is queued and the process is > the same as for module_load_q? How could it? Either the thread is waiting on module_unload_q _or_ on module_load_q. It can't wait on two queues at the same time. > To me, it looks rather error-prone. Unless it is erroneous now, at least > for future changes. Wouldn't it make sense to wake up module_load_q > along with module_unload_q in netback_changed? Or drop module_load_q > completely and use only module_unload_q (i.e. in xennet_create_dev too)? To me this looks just wrong. A thread waiting on module_load_q won't be woken up again. I'd drop module_load_q in favor of module_unload_q. Juergen