[PATCH v1 8/9] ring-buffer: Enable context analysis

[Vincent Donnefort <vdonnefort@google.com>]

Locking of some variables has proven to be fiddly recently. To mitigate
further issues, enable context analysis for the ring buffer.

This comes at the expense of a few annotations and the removal of the
helpers rb_get_mapped_buffer() and rb_put_mapped_buffer(), used in a
single place anyway.

No functional change intended.

Cc: Marco Elver <elver@google.com>
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
---
 kernel/trace/Makefile      |  2 ++
 kernel/trace/ring_buffer.c | 50 ++++++++++++++++----------------------
 2 files changed, 23 insertions(+), 29 deletions(-)

diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index b0c44f438999..165593ec4c03 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -53,6 +53,8 @@ endif
 KCOV_INSTRUMENT_trace_preemptirq.o := n
 KCOV_INSTRUMENT_trace_irqsoff.o := n
 
+CONTEXT_ANALYSIS_ring_buffer.o := y
+
 CFLAGS_bpf_trace.o := -I$(src)
 
 CFLAGS_trace_benchmark.o := -I$(src)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 82f6e3df4627..99ade8b41b53 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -6269,6 +6269,7 @@ rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
 EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
 
 static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
+	__acquires(&cpu_buffer->reader_lock)
 {
 	if (likely(!in_nmi())) {
 		raw_spin_lock(&cpu_buffer->reader_lock);
@@ -6289,14 +6290,18 @@ static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
 
 	/* Continue without locking, but disable the ring buffer */
 	atomic_inc(&cpu_buffer->record_disabled);
+	__acquire(&cpu_buffer->reader_lock);
 	return false;
 }
 
 static inline void
 rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
+	__releases(&cpu_buffer->reader_lock)
 {
 	if (likely(locked))
 		raw_spin_unlock(&cpu_buffer->reader_lock);
+	else
+		__release(&cpu_buffer->reader_lock);
 }
 
 /**
@@ -6458,11 +6463,15 @@ ring_buffer_read_start(struct trace_buffer *buffer, int cpu, gfp_t flags)
 	 */
 	if (gfpflags_allow_blocking(flags))
 		mutex_lock(&buffer->mutex);
+	else
+		__acquire(&buffer->mutex);
 
 	atomic_inc(&cpu_buffer->resize_disabled);
 
 	if (gfpflags_allow_blocking(flags))
 		mutex_unlock(&buffer->mutex);
+	else
+		__release(&buffer->mutex);
 
 	/* Holds the entire event: data and meta data. */
 	iter->event_size = rb_page_capacity(READ_ONCE(cpu_buffer->reader_page));
@@ -7648,31 +7657,6 @@ static void rb_setup_ids_meta_page(struct ring_buffer_per_cpu *cpu_buffer,
 	rb_update_meta_page(cpu_buffer);
 }
 
-static struct ring_buffer_per_cpu *
-rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu)
-{
-	struct ring_buffer_per_cpu *cpu_buffer;
-
-	if (!cpumask_test_cpu(cpu, buffer->cpumask))
-		return ERR_PTR(-EINVAL);
-
-	cpu_buffer = buffer->buffers[cpu];
-
-	mutex_lock(&cpu_buffer->mapping_lock);
-
-	if (!cpu_buffer->user_mapped) {
-		mutex_unlock(&cpu_buffer->mapping_lock);
-		return ERR_PTR(-ENODEV);
-	}
-
-	return cpu_buffer;
-}
-
-static void rb_put_mapped_buffer(struct ring_buffer_per_cpu *cpu_buffer)
-{
-	mutex_unlock(&cpu_buffer->mapping_lock);
-}
-
 /*
  * Fast-path for rb_buffer_(un)map(). Called whenever the meta-page doesn't need
  * to be set-up or torn-down.
@@ -7948,9 +7932,17 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
 	unsigned long reader_size;
 	unsigned long flags;
 
-	cpu_buffer = rb_get_mapped_buffer(buffer, cpu);
-	if (IS_ERR(cpu_buffer))
-		return (int)PTR_ERR(cpu_buffer);
+	if (!cpumask_test_cpu(cpu, buffer->cpumask))
+		return -EINVAL;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+	mutex_lock(&cpu_buffer->mapping_lock);
+
+	if (!cpu_buffer->user_mapped) {
+		mutex_unlock(&cpu_buffer->mapping_lock);
+		return -ENODEV;
+	}
 
 	raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
 
@@ -8031,7 +8023,7 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu)
 	rb_update_meta_page(cpu_buffer);
 
 	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
-	rb_put_mapped_buffer(cpu_buffer);
+	mutex_unlock(&cpu_buffer->mapping_lock);
 
 	return 0;
 }
-- 
2.56.0.567.gdb80ae8cd5-goog