[PATCH RFC 0/4] barriers using data dependency

From: Michael S. Tsirkin
Date: Wed Jan 02 2019 - 15:57:53 EST

So as explained in Documentation/memory-barriers.txt e.g.
a load followed by a store require a full memory barrier,
to avoid store being ordered before the load.
Similarly load-load requires a read memory barrier.

Thinking about it, we can actually create a data dependency
by mixing the first loaded value into the pointer being

This adds an API for this and uses it in virtio.

Written over the holiday and build tested only so far.

This patchset is also suboptimal on e.g. x86 where e.g. smp_rmb is a nop.

Sending out for early feedback/flames.

Michael S. Tsirkin (4):
include/linux/compiler*.h: fix OPTIMIZER_HIDE_VAR
include/linux/compiler.h: allow memory operands
barriers: convert a control to a data dependency
virtio: use dependent_ptr_mb

Documentation/memory-barriers.txt | 20 ++++++++++++++++++++
arch/alpha/include/asm/barrier.h | 1 +
drivers/virtio/virtio_ring.c | 6 ++++--
include/asm-generic/barrier.h | 18 ++++++++++++++++++
include/linux/compiler-clang.h | 5 ++---
include/linux/compiler-gcc.h | 4 ----
include/linux/compiler-intel.h | 4 +---
include/linux/compiler.h | 8 +++++++-
8 files changed, 53 insertions(+), 13 deletions(-)