ring-buffer: Always run per-cpu ring buffer resize with schedule_work_on()

The code for resizing the trace ring buffers has to run the per-cpu
resize on the CPU itself.  The code was using preempt_off() and
running the code for the current CPU directly, otherwise calling
schedule_work_on().

At least on RT this could result in the following:

|BUG: sleeping function called from invalid context at kernel/rtmutex.c:673
|in_atomic(): 1, irqs_disabled(): 0, pid: 607, name: bash
|3 locks held by bash/607:
|CPU: 0 PID: 607 Comm: bash Not tainted 3.12.15-rt25+ #124
|(rt_spin_lock+0x28/0x68)
|(free_hot_cold_page+0x84/0x3b8)
|(free_buffer_page+0x14/0x20)
|(rb_update_pages+0x280/0x338)
|(ring_buffer_resize+0x32c/0x3dc)
|(free_snapshot+0x18/0x38)
|(tracing_set_tracer+0x27c/0x2ac)

probably via
|cd /sys/kernel/debug/tracing/
|echo 1 > events/enable ; sleep 2
|echo 1024 > buffer_size_kb

If we just always use schedule_work_on(), there's no need for the
preempt_off().  So do that.

Link: http://lkml.kernel.org/p/1405537633-31518-1-git-send-email-cminyard@mvista.com
Reported-by: Stanislav Meduna <stano@meduna.org>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7c56c3d..35825a8 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1693,22 +1693,14 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
                        if (!cpu_buffer->nr_pages_to_update)
                                continue;
 
-                       /* The update must run on the CPU that is being updated. */
-                       preempt_disable();
-                       if (cpu == smp_processor_id() || !cpu_online(cpu)) {
+                       /* Can't run something on an offline CPU. */
+                       if (!cpu_online(cpu)) {
                                rb_update_pages(cpu_buffer);
                                cpu_buffer->nr_pages_to_update = 0;
                        } else {
-                               /*
-                                * Can not disable preemption for schedule_work_on()
-                                * on PREEMPT_RT.
-                                */
-                               preempt_enable();
                                schedule_work_on(cpu,
                                                &cpu_buffer->update_pages_work);
-                               preempt_disable();
                        }
-                       preempt_enable();
                }
 
                /* wait for all the updates to complete */
@@ -1746,22 +1738,14 @@ int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size,
 
                get_online_cpus();
 
-               preempt_disable();
-               /* The update must run on the CPU that is being updated. */
-               if (cpu_id == smp_processor_id() || !cpu_online(cpu_id))
+               /* Can't run something on an offline CPU. */
+               if (!cpu_online(cpu_id))
                        rb_update_pages(cpu_buffer);
                else {
-                       /*
-                        * Can not disable preemption for schedule_work_on()
-                        * on PREEMPT_RT.
-                        */
-                       preempt_enable();
                        schedule_work_on(cpu_id,
                                         &cpu_buffer->update_pages_work);
                        wait_for_completion(&cpu_buffer->update_done);
-                       preempt_disable();
                }
-               preempt_enable();
 
                cpu_buffer->nr_pages_to_update = 0;
                put_online_cpus();