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>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index c04c433fbc5996777b2e7e3d6c95a8bc3171b1f2..86dc353f89b99cfe66c01c9348052cab0e06f91d 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -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);