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From: Greg KH on 30 Mar 2010 20:20
2.6.32-stable review patch. If anyone has any objections, please let us know.

------------------

From: Lai Jiangshan <laijs(a)cn.fujitsu.com>

commit 52fbe9cde7fdb5c6fac196d7ebd2d92d05ef3cd4 upstream.

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.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de>

---
kernel/trace/ring_buffer.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2237,12 +2237,12 @@ ring_buffer_lock_reserve(struct ring_buf
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;

@@ -2474,11 +2474,11 @@ int ring_buffer_write(struct ring_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))


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Prev: [039/116] virtio: fix out of range array access
Next: [032/116] [PATCH] sparc64: Make prom entry spinlock NMI safe.