[PATCH 1/3] tracing: Fix race with update_max_tr_single and changing tracers

[Steven Rostedt]

From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org>

The commit 34600f0e9 "tracing: Fix race with max_tr and changing tracers"
fixed the updating of the main buffers with the race of changing
tracers, but left out the fix to the updating of just a per cpu buffer.

Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
 kernel/trace/trace.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4f1dade..7ba7fc7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -744,8 +744,11 @@ update_max_tr_single(struct trace_array *tr, struct 
task_struct *tsk, int cpu)
                return;
 
        WARN_ON_ONCE(!irqs_disabled());
-       if (WARN_ON_ONCE(!current_trace->allocated_snapshot))
+       if (!current_trace->allocated_snapshot) {
+               /* Only the nop tracer should hit this when disabling */
+               WARN_ON_ONCE(current_trace != &nop_trace);
                return;
+       }
 
        arch_spin_lock(&ftrace_max_lock);
 
-- 
1.7.10.4

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