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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2013-03-12 11:32:32 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-03-28 12:12:06 -0700
commit1e3b58b64c6574c9c8e299c68c8c4716f8dd3c21 (patch)
tree84e8d63958b4c88068b5f0011160d39f5e305d8e
parent74a523fb1759bd3afabf586740041e6d09d731c2 (diff)
tracing: Fix race in snapshot swapping
commit 2721e72dd10f71a3ba90f59781becf02638aa0d9 upstream. Although the swap is wrapped with a spin_lock, the assignment of the temp buffer used to swap is not within that lock. It needs to be moved into that lock, otherwise two swaps happening on two different CPUs, can end up using the wrong temp buffer to assign in the swap. Luckily, all current callers of the swap function appear to have their own locks. But in case something is added that allows two different callers to call the swap, then there's a chance that this race can trigger and corrupt the buffers. New code is coming soon that will allow for this race to trigger. I've Cc'd stable, so this bug will not show up if someone backports one of the changes that can trigger this bug. Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/trace/trace.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 55e4d4c5313d..681a7596b298 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -708,7 +708,7 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
void
update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
{
- struct ring_buffer *buf = tr->buffer;
+ struct ring_buffer *buf;
if (trace_stop_count)
return;
@@ -720,6 +720,7 @@ update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
}
arch_spin_lock(&ftrace_max_lock);
+ buf = tr->buffer;
tr->buffer = max_tr.buffer;
max_tr.buffer = buf;