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>

1 files changed, 4 insertions, 20 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 7c56c3d06943..35825a87d6a3 100644
--- 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();