> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuzn...@redhat.com] > Sent: Monday, March 21, 2016 1:19 AM > To: KY Srinivasan <k...@microsoft.com> > Cc: gre...@linuxfoundation.org; linux-ker...@vger.kernel.org; > de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com; > jasow...@redhat.com; sta...@vger.kernel.org > Subject: Re: [PATCH 3/5] Drivers: hv: vmbus: Fix a bug in > hv_need_to_signal_on_read() > > "K. Y. Srinivasan" <k...@microsoft.com> writes: > > > We need to issue a full memory barrier prior making a signalling > > decision. > > Any reason this should be mb()? This is pretty strong and will probably > lead to performace regression ... and, btw, we have another mb() in > hv_ringbuffer_read(). > > Could you please describe the scenarion you're trying to protect against > so we could search for a better solution?
If the reading of the pend_sz (in the function hv_need_to_signal_on_read) were to be reordered and read before we commit the new read index we could have a problem. If the host were to set the pending_sz after we have sampled pending_sz and go to sleep before we commit the read index, we could miss sending the interrupt. Regards, K. Y _______________________________________________ devel mailing list de...@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
