[lttng-dev] [PATCH lttng-modules] Fix: ACCESS_ONCE() removed in kernel 4.15
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Tue Dec 19 20:32:42 UTC 2017
----- On Dec 19, 2017, at 3:06 PM, Michael Jeanson mjeanson at efficios.com wrote:
> 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, <tng_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, <tng_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, <tng_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
I think it would be safer to use a statement-expression for this one:
# define WRITE_ONCE(x, val) ({ ACCESS_ONCE(x) = val; })
Given that WRITE_ONCE and ACCESS_ONCE evaluate to the result of the assignment,
someone could legitimately do e.g.:
int *myvar = *WRITE_ONCE(x, newptr);
Where the "*" would be applied to the ACCESS_ONCE() rather than the evaluated
value.
Makes sense ?
Thanks,
Mathieu
> +#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
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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