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Commit 021c5b34 authored by Corey Minyard's avatar Corey Minyard Committed by Steven Rostedt
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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: default avatarStanislav Meduna <stano@meduna.org>
Signed-off-by: default avatarCorey Minyard <cminyard@mvista.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 3a636388

kernel/trace/ring_buffer.c

+4 −20
Original line number Diff line number Diff line
@@ -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();