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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2e767972e99c2e8791236d10afa717b920543b70..ed3fba1d6570524ca985a92c717921b9f35db725 100644 (file)
--- 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);

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8de48bac1ce2a54aeb3948bf758212b3f0f5148b..0eddfeb05fee1349332cf30fb51ef647ff91a9a4 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -388,6 +388,7 @@ struct tracer {
        struct tracer           *next;
        struct tracer_flags     *flags;
        int                     enabled;
+       int                     ref;
        bool                    print_max;
        bool                    allow_instances;
 #ifdef CONFIG_TRACER_MAX_TRACE