From 57ccbfa6a8a79c7b84394c2097efaf7935607aa5 Mon Sep 17 00:00:00 2001
From: Michael Jeanson <mjeanson@efficios.com>
Date: Tue, 25 Aug 2020 10:56:29 -0400
Subject: [PATCH 06/10] fix: removal of [smp_]read_barrier_depends (v5.9)

See upstream commits:

  commit 76ebbe78f7390aee075a7f3768af197ded1bdfbb
  Author: Will Deacon <will@kernel.org>
  Date:   Tue Oct 24 11:22:47 2017 +0100

    locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE()

    In preparation for the removal of lockless_dereference(), which is the
    same as READ_ONCE() on all architectures other than Alpha, add an
    implicit smp_read_barrier_depends() to READ_ONCE() so that it can be
    used to head dependency chains on all architectures.

  commit 76ebbe78f7390aee075a7f3768af197ded1bdfbb
  Author: Will Deacon <will.deacon@arm.com>
  Date:   Tue Oct 24 11:22:47 2017 +0100

    locking/barriers: Add implicit smp_read_barrier_depends() to READ_ONCE()

    In preparation for the removal of lockless_dereference(), which is the
    same as READ_ONCE() on all architectures other than Alpha, add an
    implicit smp_read_barrier_depends() to READ_ONCE() so that it can be
    used to head dependency chains on all architectures.

Upstream-Status: Backport

Change-Id: Ife8880bd9378dca2972da8838f40fc35ccdfaaac
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 instrumentation/events/lttng-module/i2c.h |  4 ++--
 lib/ringbuffer/backend.h                  |  2 +-
 lib/ringbuffer/backend_internal.h         |  2 +-
 lib/ringbuffer/frontend.h                 |  4 ++--
 lib/ringbuffer/ring_buffer_frontend.c     |  4 ++--
 lib/ringbuffer/ring_buffer_iterator.c     |  2 +-
 lttng-events.c                            |  8 ++++----
 probes/lttng-kprobes.c                    |  6 +++---
 probes/lttng-kretprobes.c                 |  6 +++---
 probes/lttng-tracepoint-event-impl.h      | 12 ++++++------
 probes/lttng-uprobes.c                    |  6 +++---
 wrapper/compiler.h                        | 18 ++++++++++++++++++
 wrapper/trace-clock.h                     | 15 +++++----------
 13 files changed, 51 insertions(+), 38 deletions(-)

diff --git a/instrumentation/events/lttng-module/i2c.h b/instrumentation/events/lttng-module/i2c.h
index dcbabf6..131d134 100644
--- a/instrumentation/events/lttng-module/i2c.h
+++ b/instrumentation/events/lttng-module/i2c.h
@@ -23,7 +23,7 @@ LTTNG_TRACEPOINT_EVENT_CODE(i2c_write,
 
 	TP_code_pre(
 		tp_locvar->extract_sensitive_payload =
-			READ_ONCE(extract_sensitive_payload);
+			LTTNG_READ_ONCE(extract_sensitive_payload);
 	),
 
 	TP_FIELDS(
@@ -78,7 +78,7 @@ LTTNG_TRACEPOINT_EVENT_CODE(i2c_reply,
 
 	TP_code_pre(
 		tp_locvar->extract_sensitive_payload =
-			READ_ONCE(extract_sensitive_payload);
+			LTTNG_READ_ONCE(extract_sensitive_payload);
 	),
 
 	TP_FIELDS(
diff --git a/lib/ringbuffer/backend.h b/lib/ringbuffer/backend.h
index da937f2..43e1d47 100644
--- a/lib/ringbuffer/backend.h
+++ b/lib/ringbuffer/backend.h
@@ -156,7 +156,7 @@ 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 = READ_ONCE(src[count]);
+		c = LTTNG_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 2d6a345..1226fd8 100644
--- a/lib/ringbuffer/backend_internal.h
+++ b/lib/ringbuffer/backend_internal.h
@@ -367,7 +367,7 @@ 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 = READ_ONCE(bufb->buf_wsb[idx].id);
+	id = LTTNG_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))) {
diff --git a/lib/ringbuffer/frontend.h b/lib/ringbuffer/frontend.h
index 6f516d9..41382fe 100644
--- a/lib/ringbuffer/frontend.h
+++ b/lib/ringbuffer/frontend.h
@@ -79,7 +79,7 @@ void *channel_destroy(struct channel *chan);
 #define for_each_channel_cpu(cpu, chan)					\
 	for ((cpu) = -1;						\
 		({ (cpu) = cpumask_next(cpu, (chan)->backend.cpumask);	\
-		   smp_read_barrier_depends(); (cpu) < nr_cpu_ids; });)
+		   smp_rmb(); (cpu) < nr_cpu_ids; });)
 
 extern struct lib_ring_buffer *channel_get_ring_buffer(
 				const struct lib_ring_buffer_config *config,
@@ -155,7 +155,7 @@ static inline
 int lib_ring_buffer_is_finalized(const struct lib_ring_buffer_config *config,
 				 struct lib_ring_buffer *buf)
 {
-	int finalized = READ_ONCE(buf->finalized);
+	int finalized = LTTNG_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 3cab365..4980d20 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1074,7 +1074,7 @@ int lib_ring_buffer_snapshot(struct lib_ring_buffer *buf,
 	int finalized;
 
 retry:
-	finalized = READ_ONCE(buf->finalized);
+	finalized = LTTNG_READ_ONCE(buf->finalized);
 	/*
 	 * Read finalized before counters.
 	 */
@@ -1245,7 +1245,7 @@ int lib_ring_buffer_get_subbuf(struct lib_ring_buffer *buf,
 		return -EBUSY;
 	}
 retry:
-	finalized = READ_ONCE(buf->finalized);
+	finalized = LTTNG_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 d25db72..7b4f20a 100644
--- a/lib/ringbuffer/ring_buffer_iterator.c
+++ b/lib/ringbuffer/ring_buffer_iterator.c
@@ -46,7 +46,7 @@ restart:
 	switch (iter->state) {
 	case ITER_GET_SUBBUF:
 		ret = lib_ring_buffer_get_next_subbuf(buf);
-		if (ret && !READ_ONCE(buf->finalized)
+		if (ret && !LTTNG_READ_ONCE(buf->finalized)
 		    && config->alloc == RING_BUFFER_ALLOC_GLOBAL) {
 			/*
 			 * Use "pull" scheme for global buffers. The reader
diff --git a/lttng-events.c b/lttng-events.c
index be7e389..d719294 100644
--- a/lttng-events.c
+++ b/lttng-events.c
@@ -1719,7 +1719,7 @@ int lttng_metadata_printf(struct lttng_session *session,
 	size_t len;
 	va_list ap;
 
-	WARN_ON_ONCE(!READ_ONCE(session->active));
+	WARN_ON_ONCE(!LTTNG_READ_ONCE(session->active));
 
 	va_start(ap, fmt);
 	str = kvasprintf(GFP_KERNEL, fmt, ap);
@@ -2305,7 +2305,7 @@ int _lttng_event_metadata_statedump(struct lttng_session *session,
 {
 	int ret = 0;
 
-	if (event->metadata_dumped || !READ_ONCE(session->active))
+	if (event->metadata_dumped || !LTTNG_READ_ONCE(session->active))
 		return 0;
 	if (chan->channel_type == METADATA_CHANNEL)
 		return 0;
@@ -2377,7 +2377,7 @@ int _lttng_channel_metadata_statedump(struct lttng_session *session,
 {
 	int ret = 0;
 
-	if (chan->metadata_dumped || !READ_ONCE(session->active))
+	if (chan->metadata_dumped || !LTTNG_READ_ONCE(session->active))
 		return 0;
 
 	if (chan->channel_type == METADATA_CHANNEL)
@@ -2604,7 +2604,7 @@ int _lttng_session_metadata_statedump(struct lttng_session *session)
 	struct lttng_event *event;
 	int ret = 0;
 
-	if (!READ_ONCE(session->active))
+	if (!LTTNG_READ_ONCE(session->active))
 		return 0;
 
 	lttng_metadata_begin(session);
diff --git a/probes/lttng-kprobes.c b/probes/lttng-kprobes.c
index a44eaa1..38fb72e 100644
--- a/probes/lttng-kprobes.c
+++ b/probes/lttng-kprobes.c
@@ -31,11 +31,11 @@ int lttng_kprobes_handler_pre(struct kprobe *p, struct pt_regs *regs)
 	int ret;
 	unsigned long data = (unsigned long) p->addr;
 
-	if (unlikely(!READ_ONCE(chan->session->active)))
+	if (unlikely(!LTTNG_READ_ONCE(chan->session->active)))
 		return 0;
-	if (unlikely(!READ_ONCE(chan->enabled)))
+	if (unlikely(!LTTNG_READ_ONCE(chan->enabled)))
 		return 0;
-	if (unlikely(!READ_ONCE(event->enabled)))
+	if (unlikely(!LTTNG_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 ab98ff2..a6bcd21 100644
--- a/probes/lttng-kretprobes.c
+++ b/probes/lttng-kretprobes.c
@@ -51,11 +51,11 @@ int _lttng_kretprobes_handler(struct kretprobe_instance *krpi,
 		unsigned long parent_ip;
 	} payload;
 
-	if (unlikely(!READ_ONCE(chan->session->active)))
+	if (unlikely(!LTTNG_READ_ONCE(chan->session->active)))
 		return 0;
-	if (unlikely(!READ_ONCE(chan->enabled)))
+	if (unlikely(!LTTNG_READ_ONCE(chan->enabled)))
 		return 0;
-	if (unlikely(!READ_ONCE(event->enabled)))
+	if (unlikely(!LTTNG_READ_ONCE(event->enabled)))
 		return 0;
 
 	payload.ip = (unsigned long) krpi->rp->kp.addr;
diff --git a/probes/lttng-tracepoint-event-impl.h b/probes/lttng-tracepoint-event-impl.h
index 77b8638..72a669e 100644
--- a/probes/lttng-tracepoint-event-impl.h
+++ b/probes/lttng-tracepoint-event-impl.h
@@ -1132,11 +1132,11 @@ static void __event_probe__##_name(void *__data, _proto)		      \
 									      \
 	if (!_TP_SESSION_CHECK(session, __session))			      \
 		return;							      \
-	if (unlikely(!READ_ONCE(__session->active)))			      \
+	if (unlikely(!LTTNG_READ_ONCE(__session->active)))		      \
 		return;							      \
-	if (unlikely(!READ_ONCE(__chan->enabled)))			      \
+	if (unlikely(!LTTNG_READ_ONCE(__chan->enabled)))		      \
 		return;							      \
-	if (unlikely(!READ_ONCE(__event->enabled)))			      \
+	if (unlikely(!LTTNG_READ_ONCE(__event->enabled)))		      \
 		return;							      \
 	__lf = lttng_rcu_dereference(__session->pid_tracker.p);		      \
 	if (__lf && likely(!lttng_id_tracker_lookup(__lf, current->tgid)))    \
@@ -1225,11 +1225,11 @@ static void __event_probe__##_name(void *__data)			      \
 									      \
 	if (!_TP_SESSION_CHECK(session, __session))			      \
 		return;							      \
-	if (unlikely(!READ_ONCE(__session->active)))			      \
+	if (unlikely(!LTTNG_READ_ONCE(__session->active)))		      \
 		return;							      \
-	if (unlikely(!READ_ONCE(__chan->enabled)))			      \
+	if (unlikely(!LTTNG_READ_ONCE(__chan->enabled)))		      \
 		return;							      \
-	if (unlikely(!READ_ONCE(__event->enabled)))			      \
+	if (unlikely(!LTTNG_READ_ONCE(__event->enabled)))		      \
 		return;							      \
 	__lf = lttng_rcu_dereference(__session->pid_tracker.p);		      \
 	if (__lf && likely(!lttng_id_tracker_lookup(__lf, current->tgid)))    \
diff --git a/probes/lttng-uprobes.c b/probes/lttng-uprobes.c
index bc10128..bda1d9b 100644
--- a/probes/lttng-uprobes.c
+++ b/probes/lttng-uprobes.c
@@ -40,11 +40,11 @@ int lttng_uprobes_handler_pre(struct uprobe_consumer *uc, struct pt_regs *regs)
 		unsigned long ip;
 	} payload;
 
-	if (unlikely(!READ_ONCE(chan->session->active)))
+	if (unlikely(!LTTNG_READ_ONCE(chan->session->active)))
 		return 0;
-	if (unlikely(!READ_ONCE(chan->enabled)))
+	if (unlikely(!LTTNG_READ_ONCE(chan->enabled)))
 		return 0;
-	if (unlikely(!READ_ONCE(event->enabled)))
+	if (unlikely(!LTTNG_READ_ONCE(event->enabled)))
 		return 0;
 
 	lib_ring_buffer_ctx_init(&ctx, chan->chan, &lttng_probe_ctx,
diff --git a/wrapper/compiler.h b/wrapper/compiler.h
index 1496f33..b9f8c51 100644
--- a/wrapper/compiler.h
+++ b/wrapper/compiler.h
@@ -9,6 +9,7 @@
 #define _LTTNG_WRAPPER_COMPILER_H
 
 #include <linux/compiler.h>
+#include <linux/version.h>
 
 /*
  * Don't allow compiling with buggy compiler.
@@ -39,4 +40,21 @@
 # define WRITE_ONCE(x, val)	({ ACCESS_ONCE(x) = val; })
 #endif
 
+/*
+ * In v4.15 a smp read barrier was added to READ_ONCE to replace
+ * lockless_dereference(), replicate this behavior on prior kernels
+ * and remove calls to smp_read_barrier_depends which was dropped
+ * in v5.9.
+ */
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,15,0))
+#define LTTNG_READ_ONCE(x)	READ_ONCE(x)
+#else
+#define LTTNG_READ_ONCE(x)			\
+({						\
+	typeof(x) __val = READ_ONCE(x);		\
+	smp_read_barrier_depends();		\
+	__val;					\
+})
+#endif
+
 #endif /* _LTTNG_WRAPPER_COMPILER_H */
diff --git a/wrapper/trace-clock.h b/wrapper/trace-clock.h
index 9f4e366..187fc82 100644
--- a/wrapper/trace-clock.h
+++ b/wrapper/trace-clock.h
@@ -160,33 +160,30 @@ static inline void put_trace_clock(void)
 
 static inline u64 trace_clock_read64(void)
 {
-	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = LTTNG_READ_ONCE(lttng_trace_clock);
 
 	if (likely(!ltc)) {
 		return trace_clock_read64_monotonic();
 	} else {
-		read_barrier_depends();	/* load ltc before content */
 		return ltc->read64();
 	}
 }
 
 static inline u64 trace_clock_freq(void)
 {
-	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = LTTNG_READ_ONCE(lttng_trace_clock);
 
 	if (!ltc) {
 		return trace_clock_freq_monotonic();
 	} else {
-		read_barrier_depends();	/* load ltc before content */
 		return ltc->freq();
 	}
 }
 
 static inline int trace_clock_uuid(char *uuid)
 {
-	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = LTTNG_READ_ONCE(lttng_trace_clock);
 
-	read_barrier_depends();	/* load ltc before content */
 	/* Use default UUID cb when NULL */
 	if (!ltc || !ltc->uuid) {
 		return trace_clock_uuid_monotonic(uuid);
@@ -197,24 +194,22 @@ static inline int trace_clock_uuid(char *uuid)
 
 static inline const char *trace_clock_name(void)
 {
-	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = LTTNG_READ_ONCE(lttng_trace_clock);
 
 	if (!ltc) {
 		return trace_clock_name_monotonic();
 	} else {
-		read_barrier_depends();	/* load ltc before content */
 		return ltc->name();
 	}
 }
 
 static inline const char *trace_clock_description(void)
 {
-	struct lttng_trace_clock *ltc = READ_ONCE(lttng_trace_clock);
+	struct lttng_trace_clock *ltc = LTTNG_READ_ONCE(lttng_trace_clock);
 
 	if (!ltc) {
 		return trace_clock_description_monotonic();
 	} else {
-		read_barrier_depends();	/* load ltc before content */
 		return ltc->description();
 	}
 }
-- 
2.19.1