[tip:tracing/urgent] tracing: Use same local variable when resetting the ring buffer

[tip-bot for Steven Rostedt <srostedt@xxxxxxxxxx>]

Commit-ID:  283740c619d211e34572cc93c8cdba92ccbdb9cc
Gitweb:     http://git.kernel.org/tip/283740c619d211e34572cc93c8cdba92ccbdb9cc
Author:     Steven Rostedt <srostedt@xxxxxxxxxx>
AuthorDate: Fri, 12 Mar 2010 19:48:41 -0500
Committer:  Steven Rostedt <rostedt@xxxxxxxxxxx>
CommitDate: Fri, 12 Mar 2010 20:29:20 -0500

tracing: Use same local variable when resetting the ring buffer

In the ftrace code that resets the ring buffer it references the
buffer with a local variable, but then uses the tr->buffer as the
parameter to reset. If the wakeup tracer is running, which can
switch the tr->buffer with the max saved buffer, this can break
the requirement of disabling the buffer before the reset.

   buffer = tr->buffer;
   ring_buffer_record_disable(buffer);
   synchronize_sched();
   __tracing_reset(tr->buffer, cpu);

If the tr->buffer is swapped, then the reset is not happening to the
buffer that was disabled. This will cause the ring buffer to fail.

Found with Li Zefan's ftrace_stress_test.

Cc: stable@xxxxxxxxxx
Reported-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6af8d7b..60de37b 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -840,10 +840,10 @@ out:
 	mutex_unlock(&trace_types_lock);
 }
 
-static void __tracing_reset(struct trace_array *tr, int cpu)
+static void __tracing_reset(struct ring_buffer *buffer, int cpu)
 {
 	ftrace_disable_cpu();
-	ring_buffer_reset_cpu(tr->buffer, cpu);
+	ring_buffer_reset_cpu(buffer, cpu);
 	ftrace_enable_cpu();
 }
 
@@ -855,7 +855,7 @@ void tracing_reset(struct trace_array *tr, int cpu)
 
 	/* Make sure all commits have finished */
 	synchronize_sched();
-	__tracing_reset(tr, cpu);
+	__tracing_reset(buffer, cpu);
 
 	ring_buffer_record_enable(buffer);
 }
@@ -873,7 +873,7 @@ void tracing_reset_online_cpus(struct trace_array *tr)
 	tr->time_start = ftrace_now(tr->cpu);
 
 	for_each_online_cpu(cpu)
-		__tracing_reset(tr, cpu);
+		__tracing_reset(buffer, cpu);
 
 	ring_buffer_record_enable(buffer);
 }
--
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