tracing: Add ref count to tracer for when they are being read by pipe

When one of the trace pipe files are being read (by either the trace_pipe
or trace_pipe_raw), do not allow the current_trace to change. By adding
a ref count that is incremented when the pipe files are opened, will
prevent the current_trace from being changed.

This will allow for the removal of the global trace_types_lock from
reading the pipe buffers (which is currently a bottle neck).

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2e767972e99c..ed3fba1d6570 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4140,6 +4140,12 @@ static int tracing_set_tracer(struct trace_array *tr, const char *buf)
                 goto out;
         }
 
+        /* If trace pipe files are being read, we can't change the tracer */
+        if (tr->current_trace->ref) {
+                ret = -EBUSY;
+                goto out;
+        }
+
         trace_branch_disable();
 
         tr->current_trace->enabled--;
@@ -4363,6 +4369,8 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
                 iter->trace->pipe_open(iter);
 
         nonseekable_open(inode, filp);
+
+        tr->current_trace->ref++;
 out:
         mutex_unlock(&trace_types_lock);
         return ret;
@@ -4382,6 +4390,8 @@ static int tracing_release_pipe(struct inode *inode, struct file *file)
 
         mutex_lock(&trace_types_lock);
 
+        tr->current_trace->ref--;
+
         if (iter->trace->pipe_close)
                 iter->trace->pipe_close(iter);
 
@@ -5331,6 +5341,8 @@ static int tracing_buffers_open(struct inode *inode, struct file *filp)
 
         filp->private_data = info;
 
+        tr->current_trace->ref++;
+
         mutex_unlock(&trace_types_lock);
 
         ret = nonseekable_open(inode, filp);
@@ -5437,6 +5449,8 @@ static int tracing_buffers_release(struct inode *inode, struct file *file)
 
         mutex_lock(&trace_types_lock);
 
+        iter->tr->current_trace->ref--;
+
         __trace_array_put(iter->tr);
 
         if (info->spare)
@@ -6416,7 +6430,7 @@ static int instance_delete(const char *name)
                 goto out_unlock;
 
         ret = -EBUSY;
-        if (tr->ref)
+        if (tr->ref || (tr->current_trace && tr->current_trace->ref))
                 goto out_unlock;
 
         list_del(&tr->list);