Re: [PATCH] perf/ring_buffer: Fix invalid page order

From: Takao Indoh
Date: Tue Nov 15 2016 - 04:11:29 EST


On 2016/11/15 17:48, Ingo Molnar wrote:

* Takao Indoh <indou.takao@xxxxxxxxxxxxxx> wrote:

In rb_alloc_aux_page(), a page order is set to MAX_ORDER when order is
greater than MAX_ORDER, but page order should be less than MAX_ORDER,
therefore alloc_pages_node fails at least once. This patch fixes page
order so that it can be always less than MAX_ORDER.

Signed-off-by: Takao Indoh <indou.takao@xxxxxxxxxxxxxx>
---
kernel/events/ring_buffer.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 257fa46..3f76fdd 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -502,8 +502,8 @@ static struct page *rb_alloc_aux_page(int node, int order)
{
struct page *page;

- if (order > MAX_ORDER)
- order = MAX_ORDER;
+ if (order >= MAX_ORDER)
+ order = MAX_ORDER - 1;

do {
page = alloc_pages_node(node, PERF_AUX_GFP, order);

I'm wondering under what circumstances this allocation failure was seen in
practice - why did others not hit this?

I found this when I ran perf with -m,2048. I think in the most cases
users use default buffer size hence they does not notice.

Thanks,
Takao Indoh