[PATCH v6 04/13] tracing: Implement creating an instance based on a given memory region

Steven Rostedt
2024-06-12T23:20:06Z

Allow for creating a new instance by passing in an address and size to map
the ring buffer for the instance to.

This will allow features like a pstore memory mapped region to be used for
an tracing instance ring buffer that can be retrieved from one boot to the
next.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 50 +++++++++++++++++++++++++++++++++++---------
kernel/trace/trace.h | 6 +++++-
2 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 578a49ff5c32..ff2b504fbe00 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4921,6 +4921,11 @@ static int tracing_open(struct inode *inode, struct file *file)
static bool
trace_ok_for_array(struct tracer *t, struct trace_array *tr)
{
+#ifdef CONFIG_TRACER_SNAPSHOT
+ /* arrays with mapped buffer range do not have snapshots */
+ if (tr->range_addr_start && t->use_max_tr)
+ return false;
+#endif
return (tr->flags & TRACE_ARRAY_FL_GLOBAL) || t->allow_instances;
}

@@ -8664,11 +8669,13 @@ tracing_init_tracefs_percpu(struct trace_array *tr, long cpu)
tr, cpu, &tracing_entries_fops);

#ifdef CONFIG_TRACER_SNAPSHOT
- trace_create_cpu_file("snapshot", TRACE_MODE_WRITE, d_cpu,
- tr, cpu, &snapshot_fops);
+ if (!tr->range_addr_start) {
+ trace_create_cpu_file("snapshot", TRACE_MODE_WRITE, d_cpu,
+ tr, cpu, &snapshot_fops);

- trace_create_cpu_file("snapshot_raw", TRACE_MODE_READ, d_cpu,
- tr, cpu, &snapshot_raw_fops);
+ trace_create_cpu_file("snapshot_raw", TRACE_MODE_READ, d_cpu,
+ tr, cpu, &snapshot_raw_fops);
+ }
#endif
}

@@ -9205,7 +9212,18 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size

buf->tr = tr;

- buf->buffer = ring_buffer_alloc(size, rb_flags);
+ if (tr->range_addr_start && tr->range_addr_size) {
+ buf->buffer = ring_buffer_alloc_range(size, rb_flags, 0,
+ tr->range_addr_start,
+ tr->range_addr_size);
+ /*
+ * This is basically the same as a mapped buffer,
+ * with the same restrictions.
+ */
+ tr->mapped++;
+ } else {
+ buf->buffer = ring_buffer_alloc(size, rb_flags);
+ }
if (!buf->buffer)
return -ENOMEM;

@@ -9242,6 +9260,10 @@ static int allocate_trace_buffers(struct trace_array *tr, int size)
return ret;

#ifdef CONFIG_TRACER_MAX_TRACE
+ /* Fix mapped buffer trace arrays do not have snapshot buffers */
+ if (tr->range_addr_start)
+ return 0;
+
ret = allocate_trace_buffer(tr, &tr->max_buffer,
allocate_snapshot ? size : 1);
if (MEM_FAIL(ret, "Failed to allocate trace buffer\n")) {
@@ -9342,7 +9364,9 @@ static int trace_array_create_dir(struct trace_array *tr)
}

static struct trace_array *
-trace_array_create_systems(const char *name, const char *systems)
+trace_array_create_systems(const char *name, const char *systems,
+ unsigned long range_addr_start,
+ unsigned long range_addr_size)
{
struct trace_array *tr;
int ret;
@@ -9368,6 +9392,10 @@ trace_array_create_systems(const char *name, const char *systems)
goto out_free_tr;
}

+ /* Only for boot up memory mapped ring buffers */
+ tr->range_addr_start = range_addr_start;
+ tr->range_addr_size = range_addr_size;
+
tr->trace_flags = global_trace.trace_flags & ~ZEROED_TRACE_FLAGS;

cpumask_copy(tr->tracing_cpumask, cpu_all_mask);
@@ -9425,7 +9453,7 @@ trace_array_create_systems(const char *name, const char *systems)

static struct trace_array *trace_array_create(const char *name)
{
- return trace_array_create_systems(name, NULL);
+ return trace_array_create_systems(name, NULL, 0, 0);
}

static int instance_mkdir(const char *name)
@@ -9479,7 +9507,7 @@ struct trace_array *trace_array_get_by_name(const char *name, const char *system
goto out_unlock;
}

- tr = trace_array_create_systems(name, systems);
+ tr = trace_array_create_systems(name, systems, 0, 0);

if (IS_ERR(tr))
tr = NULL;
@@ -9672,8 +9700,10 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
MEM_FAIL(1, "Could not allocate function filter files");

#ifdef CONFIG_TRACER_SNAPSHOT
- trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer,
- tr, &snapshot_fops);
+ if (!tr->range_addr_start) {
+ trace_create_file("snapshot", TRACE_MODE_WRITE, d_tracer,
+ tr, &snapshot_fops);
+ }
#endif

trace_create_file("error_log", TRACE_MODE_WRITE, d_tracer,
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 749a182dab48..5dd48932509c 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -336,7 +336,6 @@ struct trace_array {
bool allocated_snapshot;
spinlock_t snapshot_trigger_lock;
unsigned int snapshot;
- unsigned int mapped;
unsigned long max_latency;
#ifdef CONFIG_FSNOTIFY
struct dentry *d_max_latency;
@@ -344,6 +343,11 @@ struct trace_array {
struct irq_work fsnotify_irqwork;
#endif
#endif
+ /* The below is for memory mapped ring buffer */
+ unsigned int mapped;
+ unsigned long range_addr_start;
+ unsigned long range_addr_size;
+
struct trace_pid_list __rcu *filtered_pids;
struct trace_pid_list __rcu *filtered_no_pids;
/*
--
2.43.0