Commit 7ef282e0 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

tracing: Move pipe reference to trace array instead of current_tracer 



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: cf6ab6d9 ("tracing: Add ref count to tracer for when they are being read by pipe")
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent e6bc5b3f

kernel/trace/trace.c

+6 −6
Original line number Diff line number Diff line
@@ -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);

kernel/trace/trace.h

+1 −1
Original line number Diff line number Diff line
@@ -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

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