ring-buffer: Move disabled check into preempt disable section

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@kernel.org
Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4B949E43.2010906@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 8c1b2d2..54191d6 100644 (file)
--- 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))