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

The resetting of the entire ring buffer use to simply go through and reset each individual CPU buffer that had its own protection and synchronization. But this was very slow, due to performing a synchronization for each CPU. The code was reshuffled to do one disabling of all CPU buffers, followed by a single RCU synchronization, and then the resetting of each of the CPU buffers. But unfortunately, the mutex that prevented multiple occurrences of resetting the buffer was not moved to the upper function, and there is nothing to protect from it.

Take the ring buffer mutex around the global reset.

Cc: stable@vger.kernel.org Fixes: b23d7a5f4a07a ("ring-buffer: speed up buffer resets by avoiding synchronize_rcu for each CPU") Reported-by: "Tzvetomir Stoyanov (VMware)" tz.stoyanov@gmail.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- kernel/trace/ring_buffer.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f6520d0a4c8c..2699e9e562b1 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5228,6 +5228,9 @@ void ring_buffer_reset(struct trace_buffer *buffer) struct ring_buffer_per_cpu *cpu_buffer; int cpu;

+ /* prevent another thread from changing buffer sizes */ + mutex_lock(&buffer->mutex); + for_each_buffer_cpu(buffer, cpu) { cpu_buffer = buffer->buffers[cpu];

@@ -5246,6 +5249,8 @@ void ring_buffer_reset(struct trace_buffer *buffer) atomic_dec(&cpu_buffer->record_disabled); atomic_dec(&cpu_buffer->resize_disabled); } + + mutex_unlock(&buffer->mutex); } EXPORT_SYMBOL_GPL(ring_buffer_reset);