From: "Steven Rostedt (Google)" rostedt@goodmis.org

When the ring buffer is being resized, it can cause side effects to the running tracer. For instance, there's a race with irqsoff tracer that swaps individual per cpu buffers between the main buffer and the snapshot buffer. The resize operation modifies the main buffer and then the snapshot buffer. If a swap happens in between those two operations it will break the tracer.

Simply stop the running tracer before resizing the buffers and enable it again when finished.

Cc: stable@vger.kernel.org Fixes: 3928a8a2d9808 ("ftrace: make work with new ring buffer") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/trace.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 231c173ec04f..e978868b1a22 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -6387,9 +6387,12 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr, if (!tr->array_buffer.buffer) return 0;

+ /* Do not allow tracing while resizng ring buffer */ + tracing_stop_tr(tr); + ret = ring_buffer_resize(tr->array_buffer.buffer, size, cpu); if (ret < 0) - return ret; + goto out_start;

#ifdef CONFIG_TRACER_MAX_TRACE if (!tr->current_trace->use_max_tr) @@ -6417,7 +6420,7 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr, WARN_ON(1); tracing_disabled = 1; } - return ret; + goto out_start; }

update_buffer_entries(&tr->max_buffer, cpu); @@ -6426,7 +6429,8 @@ static int __tracing_resize_ring_buffer(struct trace_array *tr, #endif /* CONFIG_TRACER_MAX_TRACE */

update_buffer_entries(&tr->array_buffer, cpu); - + out_start: + tracing_start_tr(tr); return ret; }