[for-next][PATCH 29/32] ring-buffer: Always run per-cpu ring buffer resize with schedule_work_on()

Steven Rostedt
2014-07-19T13:17:09Z

[-- Attachment #1: 0029-ring-buffer-Always-run-per-cpu-ring-buffer-resize-wi.patch --]
[-- Type: text/plain, Size: 2977 bytes --]

From: Corey Minyard <cminyard@mvista.com>

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>
---
kernel/trace/ring_buffer.c | 24 ++++--------------------
1 file 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();
--
2.0.1