[lttng-dev] [PATCH lttng-modules] Fix: ACCESS_ONCE() removed in kernel 4.15

Michael Jeanson mjeanson at efficios.com
Tue Dec 19 20:06:42 UTC 2017 

The ACCESS_ONCE() macro was removed in kernel 4.15 and should be
replaced by READ_ONCE and WRITE_ONCE which were introduced in kernel
3.19.

This commit replaces all calls to ACCESS_ONCE() with the appropriate
READ_ONCE or WRITE_ONCE and adds compatbility macros for kernels that
have them.

See this upstream commit:

  commit b03a0fe0c5e4b46dcd400d27395b124499554a71
  Author: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
  Date:   Mon Oct 23 14:07:25 2017 -0700

    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: Michael Jeanson <mjeanson at efficios.com>
---
 instrumentation/events/lttng-module/i2c.h |  4 ++--
 lib/ringbuffer/backend.h                  |  2 +-
 lib/ringbuffer/backend_internal.h         |  7 ++++---
 lib/ringbuffer/frontend.h                 |  2 +-
 lib/ringbuffer/ring_buffer_frontend.c     | 10 +++++-----
 lib/ringbuffer/ring_buffer_iterator.c     |  2 +-
 lttng-clock.c                             |  6 +++---
 lttng-events.c                            | 30 +++++++++++++++---------------
 probes/lttng-ftrace.c                     | 12 ++++++------
 probes/lttng-kprobes.c                    |  6 +++---
 probes/lttng-kretprobes.c                 | 10 +++++-----
 probes/lttng-tracepoint-event-impl.h      | 12 ++++++------
 wrapper/compiler.h                        | 13 +++++++++++++
 wrapper/trace-clock.h                     | 11 ++++++-----
 14 files changed, 71 insertions(+), 56 deletions(-)

diff --git a/instrumentation/events/lttng-module/i2c.h b/instrumentation/events/lttng-module/i2c.h
index 4088b60..dd91c9b 100644
--- a/instrumentation/events/lttng-module/i2c.h
+++ b/instrumentation/events/lttng-module/i2c.h
@@ -22,7 +22,7 @@ LTTNG_TRACEPOINT_EVENT_CODE(i2c_write,
 
 	TP_code_pre(
 		tp_locvar->extract_sensitive_payload =
-			ACCESS_ONCE(extract_sensitive_payload);
+			READ_ONCE(extract_sensitive_payload);
 	),
 
 	TP_FIELDS(
@@ -77,7 +77,7 @@ LTTNG_TRACEPOINT_EVENT_CODE(i2c_reply,
 
 	TP_code_pre(
 		tp_locvar->extract_sensitive_payload =
-			ACCESS_ONCE(extract_sensitive_payload);
+			READ_ONCE(extract_sensitive_payload);
 	),
 
 	TP_FIELDS(
diff --git a/lib/ringbuffer/backend.h b/lib/ringbuffer/backend.h
index 9db0095..0b75de8 100644
--- a/lib/ringbuffer/backend.h
+++ b/lib/ringbuffer/backend.h
@@ -169,7 +169,7 @@ size_t lib_ring_buffer_do_strcpy(const struct lib_ring_buffer_config *config,
 		 * Only read source character once, in case it is
 		 * modified concurrently.
 		 */
-		c = ACCESS_ONCE(src[count]);
+		c = READ_ONCE(src[count]);
 		if (!c)
 			break;
 		lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
diff --git a/lib/ringbuffer/backend_internal.h b/lib/ringbuffer/backend_internal.h
index 2e59b68..dc69ecf 100644
--- a/lib/ringbuffer/backend_internal.h
+++ b/lib/ringbuffer/backend_internal.h
@@ -23,6 +23,7 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include <wrapper/compiler.h>
 #include <wrapper/ringbuffer/config.h>
 #include <wrapper/ringbuffer/backend_types.h>
 #include <wrapper/ringbuffer/frontend_types.h>
@@ -171,7 +172,7 @@ void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config *config,
 		tmp |= offset << SB_ID_OFFSET_SHIFT;
 		tmp |= SB_ID_NOREF_MASK;
 		/* Volatile store, read concurrently by readers. */
-		ACCESS_ONCE(*id) = tmp;
+		WRITE_ONCE(*id, tmp);
 	}
 }
 
@@ -379,7 +380,7 @@ void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
 	 * Performing a volatile access to read the sb_pages, because we want to
 	 * read a coherent version of the pointer and the associated noref flag.
 	 */
-	id = ACCESS_ONCE(bufb->buf_wsb[idx].id);
+	id = READ_ONCE(bufb->buf_wsb[idx].id);
 	for (;;) {
 		/* This check is called on the fast path for each record. */
 		if (likely(!subbuffer_id_is_noref(config, id))) {
@@ -448,7 +449,7 @@ int update_read_sb_index(const struct lib_ring_buffer_config *config,
 	if (config->mode == RING_BUFFER_OVERWRITE) {
 		/*
 		 * Exchange the target writer subbuffer with our own unused
-		 * subbuffer. No need to use ACCESS_ONCE() here to read the
+		 * subbuffer. No need to use READ_ONCE() here to read the
 		 * old_wpage, because the value read will be confirmed by the
 		 * following cmpxchg().
 		 */
diff --git a/lib/ringbuffer/frontend.h b/lib/ringbuffer/frontend.h
index 909abc2..1450cb7 100644
--- a/lib/ringbuffer/frontend.h
+++ b/lib/ringbuffer/frontend.h
@@ -168,7 +168,7 @@ static inline
 int lib_ring_buffer_is_finalized(const struct lib_ring_buffer_config *config,
 				 struct lib_ring_buffer *buf)
 {
-	int finalized = ACCESS_ONCE(buf->finalized);
+	int finalized = READ_ONCE(buf->finalized);
 	/*
 	 * Read finalized before counters.
 	 */
diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index abd9757..0d8279b 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -983,7 +983,7 @@ void *channel_destroy(struct channel *chan)
 			 * Perform flush before writing to finalized.
 			 */
 			smp_wmb();
-			ACCESS_ONCE(buf->finalized) = 1;
+			WRITE_ONCE(buf->finalized, 1);
 			wake_up_interruptible(&buf->read_wait);
 		}
 	} else {
@@ -997,10 +997,10 @@ void *channel_destroy(struct channel *chan)
 		 * Perform flush before writing to finalized.
 		 */
 		smp_wmb();
-		ACCESS_ONCE(buf->finalized) = 1;
+		WRITE_ONCE(buf->finalized, 1);
 		wake_up_interruptible(&buf->read_wait);
 	}
-	ACCESS_ONCE(chan->finalized) = 1;
+	WRITE_ONCE(chan->finalized, 1);
 	wake_up_interruptible(&chan->hp_wait);
 	wake_up_interruptible(&chan->read_wait);
 	priv = chan->backend.priv;
@@ -1077,7 +1077,7 @@ int lib_ring_buffer_snapshot(struct lib_ring_buffer *buf,
 	int finalized;
 
 retry:
-	finalized = ACCESS_ONCE(buf->finalized);
+	finalized = READ_ONCE(buf->finalized);
 	/*
 	 * Read finalized before counters.
 	 */
@@ -1248,7 +1248,7 @@ int lib_ring_buffer_get_subbuf(struct lib_ring_buffer *buf,
 		return -EBUSY;
 	}
 retry:
-	finalized = ACCESS_ONCE(buf->finalized);
+	finalized = READ_ONCE(buf->finalized);
 	/*
 	 * Read finalized before counters.
 	 */
diff --git a/lib/ringbuffer/ring_buffer_iterator.c b/lib/ringbuffer/ring_buffer_iterator.c
index b6bec48..61eaa5b 100644
--- a/lib/ringbuffer/ring_buffer_iterator.c
+++ b/lib/ringbuffer/ring_buffer_iterator.c
@@ -61,7 +61,7 @@ restart:
 	switch (iter->state) {
 	case ITER_GET_SUBBUF:
 		ret = lib_ring_buffer_get_next_subbuf(buf);
-		if (ret && !ACCESS_ONCE(buf->finalized)
+		if (ret && !READ_ONCE(buf->finalized)
 		    && config->alloc == RING_BUFFER_ALLOC_GLOBAL) {
 			/*
 			 * Use "pull" scheme for global buffers. The reader
diff --git a/lttng-clock.c b/lttng-clock.c
index a5a7eaa..48b4be5 100644
--- a/lttng-clock.c
+++ b/lttng-clock.c
@@ -48,7 +48,7 @@ int lttng_clock_register_plugin(struct lttng_trace_clock *ltc,
 		goto end;
 	}
 	/* set clock */
-	ACCESS_ONCE(lttng_trace_clock) = ltc;
+	WRITE_ONCE(lttng_trace_clock, ltc);
 	lttng_trace_clock_mod = mod;
 end:
 	mutex_unlock(&clock_mutex);
@@ -66,7 +66,7 @@ void lttng_clock_unregister_plugin(struct lttng_trace_clock *ltc,
 	}
 	WARN_ON_ONCE(lttng_trace_clock_mod != mod);
 
-	ACCESS_ONCE(lttng_trace_clock) = NULL;
+	WRITE_ONCE(lttng_trace_clock, NULL);
 	lttng_trace_clock_mod = NULL;
 end:
 	mutex_unlock(&clock_mutex);
@@ -83,7 +83,7 @@ void lttng_clock_ref(void)
 		ret = try_module_get(lttng_trace_clock_mod);
 		if (!ret) {
 			printk(KERN_ERR "LTTng-clock cannot get clock plugin module\n");
-			ACCESS_ONCE(lttng_trace_clock) = NULL;
+			WRITE_ONCE(lttng_trace_clock, NULL);
 			lttng_trace_clock_mod = NULL;
 		}
 	}
diff --git a/lttng-events.c b/lttng-events.c
index 21c4113..75c3fb1 100644
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -186,7 +186,7 @@ void lttng_session_destroy(struct lttng_session *session)
 	int ret;
 
 	mutex_lock(&sessions_mutex);
-	ACCESS_ONCE(session->active) = 0;
+	WRITE_ONCE(session->active, 0);
 	list_for_each_entry(chan, &session->chan, list) {
 		ret = lttng_syscalls_unregister(chan);
 		WARN_ON(ret);
@@ -261,16 +261,16 @@ int lttng_session_enable(struct lttng_session *session)
 			lib_ring_buffer_clear_quiescent_channel(chan->chan);
 	}
 
-	ACCESS_ONCE(session->active) = 1;
-	ACCESS_ONCE(session->been_active) = 1;
+	WRITE_ONCE(session->active, 1);
+	WRITE_ONCE(session->been_active, 1);
 	ret = _lttng_session_metadata_statedump(session);
 	if (ret) {
-		ACCESS_ONCE(session->active) = 0;
+		WRITE_ONCE(session->active, 0);
 		goto end;
 	}
 	ret = lttng_statedump_start(session);
 	if (ret)
-		ACCESS_ONCE(session->active) = 0;
+		WRITE_ONCE(session->active, 0);
 end:
 	mutex_unlock(&sessions_mutex);
 	return ret;
@@ -286,7 +286,7 @@ int lttng_session_disable(struct lttng_session *session)
 		ret = -EBUSY;
 		goto end;
 	}
-	ACCESS_ONCE(session->active) = 0;
+	WRITE_ONCE(session->active, 0);
 
 	/* Set transient enabler state to "disabled" */
 	session->tstate = 0;
@@ -361,7 +361,7 @@ int lttng_channel_enable(struct lttng_channel *channel)
 	channel->tstate = 1;
 	lttng_session_sync_enablers(channel->session);
 	/* Set atomically the state to "enabled" */
-	ACCESS_ONCE(channel->enabled) = 1;
+	WRITE_ONCE(channel->enabled, 1);
 end:
 	mutex_unlock(&sessions_mutex);
 	return ret;
@@ -381,7 +381,7 @@ int lttng_channel_disable(struct lttng_channel *channel)
 		goto end;
 	}
 	/* Set atomically the state to "disabled" */
-	ACCESS_ONCE(channel->enabled) = 0;
+	WRITE_ONCE(channel->enabled, 0);
 	/* Set transient enabler state to "enabled" */
 	channel->tstate = 0;
 	lttng_session_sync_enablers(channel->session);
@@ -411,7 +411,7 @@ int lttng_event_enable(struct lttng_event *event)
 	case LTTNG_KERNEL_KPROBE:
 	case LTTNG_KERNEL_FUNCTION:
 	case LTTNG_KERNEL_NOOP:
-		ACCESS_ONCE(event->enabled) = 1;
+		WRITE_ONCE(event->enabled, 1);
 		break;
 	case LTTNG_KERNEL_KRETPROBE:
 		ret = lttng_kretprobes_event_enable_state(event, 1);
@@ -446,7 +446,7 @@ int lttng_event_disable(struct lttng_event *event)
 	case LTTNG_KERNEL_KPROBE:
 	case LTTNG_KERNEL_FUNCTION:
 	case LTTNG_KERNEL_NOOP:
-		ACCESS_ONCE(event->enabled) = 0;
+		WRITE_ONCE(event->enabled, 0);
 		break;
 	case LTTNG_KERNEL_KRETPROBE:
 		ret = lttng_kretprobes_event_enable_state(event, 0);
@@ -1517,7 +1517,7 @@ void lttng_session_sync_enablers(struct lttng_session *session)
 		 */
 		enabled = enabled && session->tstate && event->chan->tstate;
 
-		ACCESS_ONCE(event->enabled) = enabled;
+		WRITE_ONCE(event->enabled, enabled);
 		/*
 		 * Sync tracepoint registration with event enabled
 		 * state.
@@ -1643,7 +1643,7 @@ int lttng_metadata_printf(struct lttng_session *session,
 	va_list ap;
 	struct lttng_metadata_stream *stream;
 
-	WARN_ON_ONCE(!ACCESS_ONCE(session->active));
+	WARN_ON_ONCE(!READ_ONCE(session->active));
 
 	va_start(ap, fmt);
 	str = kvasprintf(GFP_KERNEL, fmt, ap);
@@ -2230,7 +2230,7 @@ int _lttng_event_metadata_statedump(struct lttng_session *session,
 {
 	int ret = 0;
 
-	if (event->metadata_dumped || !ACCESS_ONCE(session->active))
+	if (event->metadata_dumped || !READ_ONCE(session->active))
 		return 0;
 	if (chan->channel_type == METADATA_CHANNEL)
 		return 0;
@@ -2297,7 +2297,7 @@ int _lttng_channel_metadata_statedump(struct lttng_session *session,
 {
 	int ret = 0;
 
-	if (chan->metadata_dumped || !ACCESS_ONCE(session->active))
+	if (chan->metadata_dumped || !READ_ONCE(session->active))
 		return 0;
 
 	if (chan->channel_type == METADATA_CHANNEL)
@@ -2454,7 +2454,7 @@ int _lttng_session_metadata_statedump(struct lttng_session *session)
 	struct lttng_event *event;
 	int ret = 0;
 
-	if (!ACCESS_ONCE(session->active))
+	if (!READ_ONCE(session->active))
 		return 0;
 	if (session->metadata_dumped)
 		goto skip_session;
diff --git a/probes/lttng-ftrace.c b/probes/lttng-ftrace.c
index 9ec326e..50675a4 100644
--- a/probes/lttng-ftrace.c
+++ b/probes/lttng-ftrace.c
@@ -58,11 +58,11 @@ void lttng_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 	} payload;
 	int ret;
 
-	if (unlikely(!ACCESS_ONCE(chan->session->active)))
+	if (unlikely(!READ_ONCE(chan->session->active)))
 		return;
-	if (unlikely(!ACCESS_ONCE(chan->enabled)))
+	if (unlikely(!READ_ONCE(chan->enabled)))
 		return;
-	if (unlikely(!ACCESS_ONCE(event->enabled)))
+	if (unlikely(!READ_ONCE(event->enabled)))
 		return;
 
 	lib_ring_buffer_ctx_init(&ctx, chan->chan, &lttng_probe_ctx,
@@ -94,11 +94,11 @@ void lttng_ftrace_handler(unsigned long ip, unsigned long parent_ip, void **data
 	} payload;
 	int ret;
 
-	if (unlikely(!ACCESS_ONCE(chan->session->active)))
+	if (unlikely(!READ_ONCE(chan->session->active)))
 		return;
-	if (unlikely(!ACCESS_ONCE(chan->enabled)))
+	if (unlikely(!READ_ONCE(chan->enabled)))
 		return;
-	if (unlikely(!ACCESS_ONCE(event->enabled)))
+	if (unlikely(!READ_ONCE(event->enabled)))
 		return;
 
 	lib_ring_buffer_ctx_init(&ctx, chan->chan, &lttng_probe_ctx,
diff --git a/probes/lttng-kprobes.c b/probes/lttng-kprobes.c
index daf14ce..b58a09b 100644
--- a/probes/lttng-kprobes.c
+++ b/probes/lttng-kprobes.c
@@ -43,11 +43,11 @@ int lttng_kprobes_handler_pre(struct kprobe *p, struct pt_regs *regs)
 	int ret;
 	unsigned long data = (unsigned long) p->addr;
 
-	if (unlikely(!ACCESS_ONCE(chan->session->active)))
+	if (unlikely(!READ_ONCE(chan->session->active)))
 		return 0;
-	if (unlikely(!ACCESS_ONCE(chan->enabled)))
+	if (unlikely(!READ_ONCE(chan->enabled)))
 		return 0;
-	if (unlikely(!ACCESS_ONCE(event->enabled)))
+	if (unlikely(!READ_ONCE(event->enabled)))
 		return 0;
 
 	lib_ring_buffer_ctx_init(&ctx, chan->chan, &lttng_probe_ctx, sizeof(data),
diff --git a/probes/lttng-kretprobes.c b/probes/lttng-kretprobes.c
index 498df62..49b7de8 100644
--- a/probes/lttng-kretprobes.c
+++ b/probes/lttng-kretprobes.c
@@ -63,11 +63,11 @@ int _lttng_kretprobes_handler(struct kretprobe_instance *krpi,
 		unsigned long parent_ip;
 	} payload;
 
-	if (unlikely(!ACCESS_ONCE(chan->session->active)))
+	if (unlikely(!READ_ONCE(chan->session->active)))
 		return 0;
-	if (unlikely(!ACCESS_ONCE(chan->enabled)))
+	if (unlikely(!READ_ONCE(chan->enabled)))
 		return 0;
-	if (unlikely(!ACCESS_ONCE(event->enabled)))
+	if (unlikely(!READ_ONCE(event->enabled)))
 		return 0;
 
 	payload.ip = (unsigned long) krpi->rp->kp.addr;
@@ -304,8 +304,8 @@ int lttng_kretprobes_event_enable_state(struct lttng_event *event,
 	}
 	lttng_krp = event->u.kretprobe.lttng_krp;
 	event_return = lttng_krp->event[EVENT_RETURN];
-	ACCESS_ONCE(event->enabled) = enable;
-	ACCESS_ONCE(event_return->enabled) = enable;
+	WRITE_ONCE(event->enabled, enable);
+	WRITE_ONCE(event_return->enabled, enable);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(lttng_kretprobes_event_enable_state);
diff --git a/probes/lttng-tracepoint-event-impl.h b/probes/lttng-tracepoint-event-impl.h
index 7ec0d75..61f1c2d 100644
--- a/probes/lttng-tracepoint-event-impl.h
+++ b/probes/lttng-tracepoint-event-impl.h
@@ -1143,11 +1143,11 @@ static void __event_probe__##_name(void *__data, _proto)		      \
 									      \
 	if (!_TP_SESSION_CHECK(session, __session))			      \
 		return;							      \
-	if (unlikely(!ACCESS_ONCE(__session->active)))			      \
+	if (unlikely(!READ_ONCE(__session->active)))			      \
 		return;							      \
-	if (unlikely(!ACCESS_ONCE(__chan->enabled)))			      \
+	if (unlikely(!READ_ONCE(__chan->enabled)))			      \
 		return;							      \
-	if (unlikely(!ACCESS_ONCE(__event->enabled)))			      \
+	if (unlikely(!READ_ONCE(__event->enabled)))			      \
 		return;							      \
 	__lpf = lttng_rcu_dereference(__session->pid_tracker);		      \
 	if (__lpf && likely(!lttng_pid_tracker_lookup(__lpf, current->tgid))) \
@@ -1217,11 +1217,11 @@ static void __event_probe__##_name(void *__data)			      \
 									      \
 	if (!_TP_SESSION_CHECK(session, __session))			      \
 		return;							      \
-	if (unlikely(!ACCESS_ONCE(__session->active)))			      \
+	if (unlikely(!READ_ONCE(__session->active)))			      \
 		return;							      \
-	if (unlikely(!ACCESS_ONCE(__chan->enabled)))			      \
+	if (unlikely(!READ_ONCE(__chan->enabled)))			      \
 		return;							      \
-	if (unlikely(!ACCESS_ONCE(__event->enabled)))			      \
+	if (unlikely(!READ_ONCE(__event->enabled)))			      \
 		return;							      \
 	__lpf = lttng_rcu_dereference(__session->pid_tracker);		      \
 	if (__lpf && likely(!lttng_pid_tracker_lookup(__lpf, current->pid)))  \
diff --git a/wrapper/compiler.h b/wrapper/compiler.h
index 0c01632..060698f 100644
--- a/wrapper/compiler.h
+++ b/wrapper/compiler.h
@@ -39,4 +39,17 @@
 # endif
 #endif
 
+/*
+ * READ/WRITE_ONCE were introduced in kernel 3.19 and ACCESS_ONCE
+ * was removed in 4.15. Prefer READ/WRITE but fallback to ACCESS
+ * when they are not available.
+ */
+#ifndef READ_ONCE
+# define READ_ONCE(x) ACCESS_ONCE(x)
+#endif
+
+#ifndef WRITE_ONCE
+# define WRITE_ONCE(x, val) ACCESS_ONCE(x) = val
+#endif
+
 #endif /* _LTTNG_WRAPPER_COMPILER_H */
diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index 7f17ccd..08f9922 100644
--- a/wrapper/trace-clock.h
+++ b/wrapper/trace-clock.h
@@ -37,6 +37,7 @@
 #include <asm/local.h>
 #include <lttng-kernel-version.h>
 #include <lttng-clock.h>
+#include <wrapper/compiler.h>
 #include <wrapper/percpu-defs.h>
 #include <wrapper/random.h>
 
@@ -176,7 +177,7 @@ static inline void put_trace_clock(void)
 
 static inline u64 trace_clock_read64(void)
 {
-	struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 
 	if (likely(!ltc)) {
 		return trace_clock_read64_monotonic();
@@ -188,7 +189,7 @@ static inline u64 trace_clock_read64(void)
 
 static inline u64 trace_clock_freq(void)
 {
-	struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 
 	if (!ltc) {
 		return trace_clock_freq_monotonic();
@@ -200,7 +201,7 @@ static inline u64 trace_clock_freq(void)
 
 static inline int trace_clock_uuid(char *uuid)
 {
-	struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 
 	read_barrier_depends();	/* load ltc before content */
 	/* Use default UUID cb when NULL */
@@ -213,7 +214,7 @@ static inline int trace_clock_uuid(char *uuid)
 
 static inline const char *trace_clock_name(void)
 {
-	struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 
 	if (!ltc) {
 		return trace_clock_name_monotonic();
@@ -225,7 +226,7 @@ static inline const char *trace_clock_name(void)
 
 static inline const char *trace_clock_description(void)
 {
-	struct lttng_trace_clock *ltc = ACCESS_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
 
 	if (!ltc) {
 		return trace_clock_description_monotonic();
-- 
2.7.4

More information about the lttng-dev mailing list