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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: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Steven Rostedt 2008-11-12 00:01:26 -05:00 committed by Ingo Molnar
parent d06bbd6695
commit 642edba5f5
1 changed files with 17 additions and 12 deletions
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29
kernel/trace/ring_buffer.c
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@ -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);