From b03a0fe0c5e4b46dcd400d27395b124499554a71 Mon Sep 17 00:00:00 2001 From: Paul E. McKenney Date: Mon, 23 Oct 2017 14:07:25 -0700 Subject: locking/atomics, mm: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the mm code and comments to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Paul E. McKenney Acked-by: Will Deacon Acked-by: Mark Rutland Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: viro@zeniv.linux.org.uk Link: http://lkml.kernel.org/r/1508792849-3115-15-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- mm/memory.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'mm/memory.c') diff --git a/mm/memory.c b/mm/memory.c index a728bed16c20..cae514e7dcfc 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3891,9 +3891,9 @@ static int handle_pte_fault(struct vm_fault *vmf) /* * some architectures can have larger ptes than wordsize, * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and - * CONFIG_32BIT=y, so READ_ONCE or ACCESS_ONCE cannot guarantee - * atomic accesses. The code below just needs a consistent - * view for the ifs and we later double check anyway with the + * CONFIG_32BIT=y, so READ_ONCE cannot guarantee atomic + * accesses. The code below just needs a consistent view + * for the ifs and we later double check anyway with the * ptl lock held. So here a barrier will do. */ barrier(); -- cgit v1.2.3-55-g7522