Commit 54f7be5b authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt
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ring-buffer: Fix NULL pointer if rb_set_head_page() fails 



The function rb_set_head_page() searches the list of ring buffer
pages for a the page that has the HEAD page flag set. If it does
not find it, it will do a WARN_ON(), disable the ring buffer and
return NULL, as this should never happen.

But if this bug happens to happen, not all callers of this function
can handle a NULL pointer being returned from it. That needs to be
fixed.

Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 70f77b3f

kernel/trace/ring_buffer.c

+7 −2
Original line number Diff line number Diff line
@@ -1396,6 +1396,8 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer) 
		struct list_head *head_page_with_bit;



		head_page = &rb_set_head_page(cpu_buffer)->list;

		if (!head_page)

			break;

		prev_page = head_page->prev;



		first_page = pages->next;
@@ -2934,7 +2936,7 @@ unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu) 
	unsigned long flags;

	struct ring_buffer_per_cpu *cpu_buffer;

	struct buffer_page *bpage;

	unsigned long ret;

	unsigned long ret = 0;



	if (!cpumask_test_cpu(cpu, buffer->cpumask))

		return 0;
@@ -2949,6 +2951,7 @@ unsigned long ring_buffer_oldest_event_ts(struct ring_buffer *buffer, int cpu) 
		bpage = cpu_buffer->reader_page;

	else

		bpage = rb_set_head_page(cpu_buffer);

	if (bpage)

		ret = bpage->page->time_stamp;

	raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
@@ -3260,6 +3263,8 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) 
	 * Splice the empty reader page into the list around the head.

	 */

	reader = rb_set_head_page(cpu_buffer);

	if (!reader)

		goto out;

	cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);

	cpu_buffer->reader_page->list.prev = reader->list.prev;