> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com] > Sent: Thursday, December 15, 2016 6:32 AM > To: Olaf Hering <o...@aepfle.de> > Cc: KY Srinivasan <k...@microsoft.com>; gre...@linuxfoundation.org; linux- > ker...@vger.kernel.org; de...@linuxdriverproject.org > Subject: Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to > kdump kernel > > Olaf Hering <o...@aepfle.de> writes: > > > On Thu, Dec 15, Vitaly Kuznetsov wrote: > > > >> vmbus_wait_for_unload() may be receiving a message (not necessarily > the > >> CHANNELMSG_UNLOAD_RESPONSE, we may see some other message) > on the same > >> CPU it runs and in this case wrmsrl() makes sense. In other cases it > >> does nothing (neither good nor bad). > > > > If that other cpu has interrupts disabled it may not process a pending > > msg (the response may be stuck in the host queue?), and the loop can not > > kick the other cpus queue if a wrmsrl is just valid for the current cpu. > > If thats true, the response will not arrive in the loop. > > > > In case interrupts get permanently disabled on the CPU which is supposed > to receive the CHANNELMSG_UNLOAD_RESPONSE message *and* there is > some > other message pedning in the slot for that CPU we'll hang. We may try to > overcome this by sending NMIs but this is getting more and more > complicated... > > I'd like to see a simple fix from Hyper-V host team: always deliver > CHANNELMSG_UNLOAD_RESPONSE reply to the cpu which sent > CHANNELMSG_UNLOAD > request. This would allow us to remove all the craziness.
Agreed; I will give this feedback to the Hyper-V guys. K. Y > > -- > Vitaly
