[for-next][PATCH 09/18] tracing: Move pipe reference to trace array instead of current_tracer

Steven Rostedt
2020-07-02T21:59:18Z

If a process has the trace_pipe open on a trace_array, the current tracer
for that trace array should not be changed. This was original enforced by a
global lock, but when instances were introduced, it was moved to the
current_trace. But this structure is shared by all instances, and a
trace_pipe is for a single instance. There's no reason that a process that
has trace_pipe open on one instance should prevent another instance from
changing its current tracer. Move the reference counter to the trace_array
instead.

This is marked as "Fixes" but is more of a clean up than a true fix.
Backport if you want, but its not critical.

Fixes: cf6ab6d9143b1 ("tracing: Add ref count to tracer for when they are being read by pipe")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
kernel/trace/trace.c | 12 ++++++------
kernel/trace/trace.h | 2 +-
2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8241d1448d70..64c5b8146cca 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5891,7 +5891,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
}

/* If trace pipe files are being read, we can't change the tracer */
- if (tr->current_trace->ref) {
+ if (tr->trace_ref) {
ret = -EBUSY;
goto out;
}
@@ -6107,7 +6107,7 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)

nonseekable_open(inode, filp);

- tr->current_trace->ref++;
+ tr->trace_ref++;
out:
mutex_unlock(&trace_types_lock);
return ret;
@@ -6126,7 +6126,7 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)

mutex_lock(&trace_types_lock);

- tr->current_trace->ref--;
+ tr->trace_ref--;

if (iter->trace->pipe_close)
iter->trace->pipe_close(iter);
@@ -7428,7 +7428,7 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)

filp->private_data = info;

- tr->current_trace->ref++;
+ tr->trace_ref++;

mutex_unlock(&trace_types_lock);

@@ -7529,7 +7529,7 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)

mutex_lock(&trace_types_lock);

- iter->tr->current_trace->ref--;
+ iter->tr->trace_ref--;

__trace_array_put(iter->tr);

@@ -8737,7 +8737,7 @@ static int __remove_instance(struct trace_array *tr)
int i;

/* Reference counter for a newly created trace array = 1. */
- if (tr->ref > 1 || (tr->current_trace && tr->current_trace->ref))
+ if (tr->ref > 1 || (tr->current_trace && tr->trace_ref))
return -EBUSY;

list_del(&tr->list);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 13db4000af3f..f21607f87189 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -356,6 +356,7 @@ struct trace_array {
struct trace_event_file *trace_marker_file;
cpumask_var_t tracing_cpumask; /* only trace on set CPUs */
int ref;
+ int trace_ref;
#ifdef CONFIG_FUNCTION_TRACER
struct ftrace_ops *ops;
struct trace_pid_list __rcu *function_pids;
@@ -547,7 +548,6 @@ struct tracer {
struct tracer *next;
struct tracer_flags *flags;
int enabled;
- int ref;
bool print_max;
bool allow_instances;
#ifdef CONFIG_TRACER_MAX_TRACE
--
2.26.2