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SubjectRe: [PATCH 1/2] ring-buffer: Fix NULL pointer if rb_set_head_page() fails
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On Fri, 2012-11-30 at 11:12 -0500, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> 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+

Hmm, quilt didn't Cc. Grumble, I think a system update of quilt removed
my modification to not have quilt get confused by the hash symbol :-(

-- Steve

> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> kernel/trace/ring_buffer.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index b979426..ec01803 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -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;
>




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