From 94bbc9c1a0b0967509f8ad91323245aad30572f7 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 23 Oct 2017 14:07:20 -0700 Subject: [PATCH] locking/atomics, samples/mic/mpssd/mpssd.c: 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. The bulk of the kernel code can be transformed via Coccinelle to use {READ,WRITE}_ONCE(), though this only modifies users of ACCESS_ONCE(), and not the implementation itself. As such, it has the potential to break homebrew ACCESS_ONCE() macros seen in some user code in the kernel tree (e.g. the virtio code, as fixed in commit ea9156fb3b71d9f7). To avoid fragility if/when that transformation occurs, and to align with the preferred usage of {READ,WRITE}_ONCE(), this patch updates the MPSSD sample code to use READ_ONCE() rather than ACCESS_ONCE(). There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland Signed-off-by: Paul E. McKenney Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Shuah Khan Cc: Thomas Gleixner Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: viro@zeniv.linux.org.uk Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1508792849-3115-10-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- samples/mic/mpssd/mpssd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/samples/mic/mpssd/mpssd.c b/samples/mic/mpssd/mpssd.c index 49db1def1721..f42ce551bb48 100644 --- a/samples/mic/mpssd/mpssd.c +++ b/samples/mic/mpssd/mpssd.c @@ -65,7 +65,7 @@ static struct mic_info mic_list; /* to align the pointer to the (next) page boundary */ #define PAGE_ALIGN(addr) _ALIGN(addr, PAGE_SIZE) -#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +#define READ_ONCE(x) (*(volatile typeof(x) *)&(x)) #define GSO_ENABLED 1 #define MAX_GSO_SIZE (64 * 1024) @@ -382,7 +382,7 @@ disp_iovec(struct mic_info *mic, struct mic_copy_desc *copy, static inline __u16 read_avail_idx(struct mic_vring *vr) { - return ACCESS_ONCE(vr->info->avail_idx); + return READ_ONCE(vr->info->avail_idx); } static inline void txrx_prepare(int type, bool tx, struct mic_vring *vr, @@ -523,7 +523,7 @@ spin_for_descriptors(struct mic_info *mic, struct mic_vring *vr) { __u16 avail_idx = read_avail_idx(vr); - while (avail_idx == le16toh(ACCESS_ONCE(vr->vr.avail->idx))) { + while (avail_idx == le16toh(READ_ONCE(vr->vr.avail->idx))) { #ifdef DEBUG mpsslog("%s %s waiting for desc avail %d info_avail %d\n", mic->name, __func__,