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Subject[PATCH 1/2] [PATCH 1/2] ring-buffer: Synchronize resizing buffer with reader lock
From: Lai Jiangshan <laijs@cn.fujitsu.com>

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>
---
kernel/trace/ring_buffer.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
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);

--
1.6.3.3



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