Ping, I haven't heard anything on this.
-corey
On 07/16/2014 02:07 PM, minyard@xxxxxxx wrote:
> From: Corey Minyard <cminyard@xxxxxxxxxx>
>
> 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.
>
> Reported-by: Stanislav Meduna <stano@xxxxxxxxxx>
> Signed-off-by: Corey Minyard <cminyard@xxxxxxxxxx>
> ---
> 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 7c56c3d..35825a8 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();
--
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