KY Srinivasan <kys@xxxxxxxxxxxxx> writes: >> -----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 these are two reads we can add a lightweight barrier just preventing compiler from reordering (e.g. smp_rmb()), right? > 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. so write and then we read and we need to prevent reordering... not sure how to get rid on mb() then ... -- Vitaly _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
