Commit-ID: 94bbc9c1a0b0967509f8ad91323245aad30572f7
Gitweb: https://git.kernel.org/tip/94bbc9c1a0b0967509f8ad91323245aad30572f7
Author: Mark Rutland <mark.rutl...@arm.com>
AuthorDate: Mon, 23 Oct 2017 14:07:20 -0700
Committer: Ingo Molnar <mi...@kernel.org>
CommitDate: Wed, 25 Oct 2017 11:01:01 +0200
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 <mark.rutl...@arm.com>
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Shuah Khan <sh...@kernel.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: da...@davemloft.net
Cc: linux-a...@vger.kernel.org
Cc: m...@ellerman.id.au
Cc: snit...@redhat.com
Cc: thor.tha...@linux.intel.com
Cc: t...@kernel.org
Cc: v...@zeniv.linux.org.uk
Cc: will.dea...@arm.com
Link:
http://lkml.kernel.org/r/1508792849-3115-10-git-send-email-paul...@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
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 49db1de..f42ce55 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__,
