[lttng-dev] [PATCH lttng-modules] Fix: ACCESS_ONCE() removed in kernel 4.15
Michael Jeanson
mjeanson at efficios.com
Tue Dec 19 20:41:34 UTC 2017
On 2017-12-19 15:32, Mathieu Desnoyers wrote:
> ----- 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 ?
Sure, you can merge the modified version or do you prefer a v2 patch?
>
> 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
>
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