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Commit 642edba5 authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
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ring-buffer: fix deadlock from reader_lock in read_start 



Impact: deadlock fix in ring_buffer_read_start

The ring_buffer_iter_reset was called from ring_buffer_read_start
where both grabbed the reader_lock.

This patch separates out the internals of ring_buffer_iter_reset
to its own function so that both APIs may grab the reader_lock.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent d06bbd66

kernel/trace/ring_buffer.c

+17 −12
Original line number Diff line number Diff line
@@ -1475,19 +1475,9 @@ unsigned long ring_buffer_overruns(struct ring_buffer *buffer) 
	return overruns;

}



/**

 * ring_buffer_iter_reset - reset an iterator

 * @iter: The iterator to reset

 *

 * Resets the iterator, so that it will start from the beginning

 * again.

 */

void ring_buffer_iter_reset(struct ring_buffer_iter *iter)

static void rb_iter_reset(struct ring_buffer_iter *iter)

{

	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;

	unsigned long flags;



	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);



	/* Iterator usage is expected to have record disabled */

	if (list_empty(&cpu_buffer->reader_page->list)) {
@@ -1501,7 +1491,22 @@ void ring_buffer_iter_reset(struct ring_buffer_iter *iter) 
		iter->read_stamp = cpu_buffer->read_stamp;

	else

		iter->read_stamp = iter->head_page->time_stamp;

}



/**

 * ring_buffer_iter_reset - reset an iterator

 * @iter: The iterator to reset

 *

 * Resets the iterator, so that it will start from the beginning

 * again.

 */

void ring_buffer_iter_reset(struct ring_buffer_iter *iter)

{

	struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;

	unsigned long flags;



	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

	rb_iter_reset(iter);

	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);

}
@@ -1957,7 +1962,7 @@ ring_buffer_read_start(struct ring_buffer *buffer, int cpu) 


	spin_lock_irqsave(&cpu_buffer->reader_lock, flags);

	__raw_spin_lock(&cpu_buffer->lock);

	ring_buffer_iter_reset(iter);

	rb_iter_reset(iter);

	__raw_spin_unlock(&cpu_buffer->lock);

	spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);