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authorMark Rutland <mark.rutland@arm.com>2017-10-23 14:07:20 -0700
committerIngo Molnar <mingo@kernel.org>2017-10-25 11:01:01 +0200
commit94bbc9c1a0b0967509f8ad91323245aad30572f7 (patch)
treeed1d85c423bb22ef61ff0baeab732246f308ed63 /samples
parentef4d9af62f47e3070b00c3307a4d8eb5092bb9a2 (diff)
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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.rutland@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Shuah Khan <shuah@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
Diffstat (limited to 'samples')
-rw-r--r--samples/mic/mpssd/mpssd.c6
1 files 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__,