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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: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2012-11-29 22:27:22 -05:00 committed by Steven Rostedt
parent 70f77b3f7e
commit 54f7be5b83
1 changed files with 7 additions and 2 deletions
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9
kernel/trace/ring_buffer.c
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@ -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;
@ -2949,7 +2951,8 @@ 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);
ret = bpage->page->time_stamp;
if (bpage)
ret = bpage->page->time_stamp;
raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return ret;
@ -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;