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Subject[for-next][PATCH 1/2] tracing: Add ref count to tracer for when they are being read by pipe
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

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>
---
kernel/trace/trace.c | 16 +++++++++++++++-
kernel/trace/trace.h | 1 +
2 files changed, 16 insertions(+), 1 deletion(-)

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);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 8de48bac1ce2..0eddfeb05fee 100644
--- 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
--
2.1.3



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