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From: Steven Rostedt on 12 Mar 2010 22:10
From: Lai Jiangshan <laijs(a)cn.fujitsu.com>

The ring buffer resizing and resetting relies on a schedule RCU
action. The buffers are disabled, a synchronize_sched() is called
and then the resize or reset takes place.

But this only works if the disabling of the buffers are within the
preempt disabled section, otherwise a window exists that the buffers
can be written to while a reset or resize takes place.

Cc: stable(a)kernel.org
Reported-by: Li Zefan <lizf(a)cn.fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs(a)cn.fujitsu.com>
LKML-Reference: <4B949E43.2010906(a)cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt(a)goodmis.org>
---
kernel/trace/ring_buffer.c | 12 ++++++------
1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 8c1b2d2..54191d6 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2232,12 +2232,12 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length)
if (ring_buffer_flags != RB_BUFFERS_ON)
return NULL;

- if (atomic_read(&buffer->record_disabled))
- return NULL;
-
/* If we are tracing schedule, we don't want to recurse */
resched = ftrace_preempt_disable();

+ if (atomic_read(&buffer->record_disabled))
+ goto out_nocheck;
+
if (trace_recursive_lock())
goto out_nocheck;

@@ -2469,11 +2469,11 @@ int ring_buffer_write(struct ring_buffer *buffer,
if (ring_buffer_flags != RB_BUFFERS_ON)
return -EBUSY;

- if (atomic_read(&buffer->record_disabled))
- return -EBUSY;
-
resched = ftrace_preempt_disable();

+ if (atomic_read(&buffer->record_disabled))
+ goto out;
+
cpu = raw_smp_processor_id();

if (!cpumask_test_cpu(cpu, buffer->cpumask))
--
1.7.0


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Prev: [PATCH 5/5] tracing: Do not record user stack trace from NMI context
Next: [PATCH 2/5] function-graph: Init curr_ret_stack with ret_stack