3.2-stable review patch. If anyone has any objections, please let me know.
------------------
From: Steven Rostedt <srost...@redhat.com>
commit 54f7be5b831254199522523ccab4c3d954bbf576 upstream.
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.
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
kernel/trace/ring_buffer.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2683,7 +2683,7 @@ unsigned long ring_buffer_oldest_event_t
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;
@@ -2698,7 +2698,8 @@ unsigned long ring_buffer_oldest_event_t
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;
@@ -3005,6 +3006,8 @@ rb_get_reader_page(struct ring_buffer_pe
* 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;
--
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