The following commit has been merged in the linux branch: commit f7112949f6a4cd6883d66c882d568c2197321de6 Author: Lai Jiangshan laijs@cn.fujitsu.com Date: Tue Nov 3 19:42:45 2009 +0800

ring-buffer: Synchronize resizing buffer with reader lock

We got a sudden panic when we reduced the size of the ringbuffer.

We can reproduce the panic by the following steps:

echo 1 > events/sched/enable cat trace_pipe > /dev/null &

while ((1)) do echo 12000 > buffer_size_kb echo 512 > buffer_size_kb done

(not more than 5 seconds, panic ...)

Reported-by: KOSAKI Motohiro kosaki.motohiro@jp.fujitsu.com Signed-off-by: Lai Jiangshan laijs@cn.fujitsu.com LKML-Reference: 4AF01735.9060409@cn.fujitsu.com Signed-off-by: Steven Rostedt rostedt@goodmis.org

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 3ffa502..5dd017f 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1193,6 +1193,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages) atomic_inc(&cpu_buffer->record_disabled); synchronize_sched();

+ spin_lock_irq(&cpu_buffer->reader_lock); rb_head_page_deactivate(cpu_buffer);

for (i = 0; i < nr_pages; i++) { @@ -1207,6 +1208,7 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages) return;

rb_reset_cpu(cpu_buffer); + spin_unlock_irq(&cpu_buffer->reader_lock);

rb_check_pages(cpu_buffer);