> -----Original Message----- > From: Vitaly Kuznetsov [mailto:vkuznets@xxxxxxxxxx] > Sent: Monday, March 21, 2016 1:19 AM > To: KY Srinivasan <kys@xxxxxxxxxxxxx> > Cc: gregkh@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; > devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; > jasowang@xxxxxxxxxx; stable@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 3/5] Drivers: hv: vmbus: Fix a bug in > hv_need_to_signal_on_read() > > "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> 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 devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
