From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH 0/3] virtio/vringh: kill off ACCESS_ONCE() Date: Thu, 24 Nov 2016 22:36:58 +0200 Message-ID: <20161124222357-mutt-send-email-mst@kernel.org> References: <1479983114-17190-1-git-send-email-mark.rutland@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: dave@stgolabs.net, kvm@vger.kernel.org, dbueso@suse.de, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, paulmck@linux.vnet.ibm.com, dvyukov@google.com To: Mark Rutland Return-path: Content-Disposition: inline In-Reply-To: <1479983114-17190-1-git-send-email-mark.rutland@arm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org On Thu, Nov 24, 2016 at 10:25:11AM +0000, Mark Rutland wrote: > For several reasons, it would be beneficial to kill off ACCESS_ONCE() > tree-wide, in favour of {READ,WRITE}_ONCE(). These work with aggregate types, > more obviously document their intended behaviour, and are necessary for tools > like KTSAN to work correctly (as otherwise reads and writes cannot be > instrumented separately). > > While it's possible to script the bulk of this tree-wide conversion, some cases > such as the virtio code, require some manual intervention. This series moves > the virtio and vringh code over to {READ,WRITE}_ONCE(), in the process fixing a > bug in the virtio headers. > > Thanks, > Mark. I don't have a problem with this specific patchset. Though I really question the whole _ONCE APIs esp with aggregate types - these seem to generate a memcpy and an 8-byte read/writes sometimes, and I'm pretty sure this simply can't be read/written at once on all architectures. So I worry it's kind of like volatile in this respect, too easy to overuse. > Mark Rutland (3): > tools/virtio: fix READ_ONCE() > vringh: kill off ACCESS_ONCE() > tools/virtio: use {READ,WRITE}_ONCE() in uaccess.h > > drivers/vhost/vringh.c | 5 +++-- > tools/virtio/linux/compiler.h | 2 +- > tools/virtio/linux/uaccess.h | 9 +++++---- > 3 files changed, 9 insertions(+), 7 deletions(-) > > -- > 2.7.4