Re: [PATCH 1/8] ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2015-01-15 23:09:35
Also in:
kvm, linux-arch, linux-mm, lkml
On Thu, 2015-01-15 at 09:58 +0100, Christian Borntraeger wrote:
quoted hunk ↗ jump to hunk
ACCESS_ONCE does not work reliably on non-scalar types. For example gcc 4.6 and 4.7 might remove the volatile tag for such accesses during the SRA (scalar replacement of aggregates) step (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145) Change the ppc/kvm code to replace ACCESS_ONCE with READ_ONCE. Signed-off-by: Christian Borntraeger <redacted> --- arch/powerpc/kvm/book3s_hv_rm_xics.c | 8 ++++---- arch/powerpc/kvm/book3s_xics.c | 16 ++++++++-------- 2 files changed, 12 insertions(+), 12 deletions(-)diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c b/arch/powerpc/kvm/book3s_hv_rm_xics.c index 7b066f6..7c22997 100644 --- a/arch/powerpc/kvm/book3s_hv_rm_xics.c +++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c@@ -152,7 +152,7 @@ static void icp_rm_down_cppr(struct kvmppc_xics *xics, struct kvmppc_icp *icp, * in virtual mode. */ do { - old_state = new_state = ACCESS_ONCE(icp->state); + old_state = new_state = READ_ONCE(icp->state);
These are all icp->state. Which is a union, but it's only the size of unsigned long. So in practice there shouldn't be a bug here right? cheers