On 09/12/2018 09:51 AM, John Fastabend wrote:
On 09/12/2018 09:21 AM, Tushar Dave wrote:
On 09/11/2018 12:38 PM, Tushar Dave wrote:
Helper bpg_msg_pull_data() can allocate multiple pages while
linearizing multiple scatterlist elements into one shared page.
However, if the shared page has size > PAGE_SIZE, using
copy_page_to_iter() causes below warning.
e.g.
[ 6367.019832] WARNING: CPU: 2 PID: 7410 at lib/iov_iter.c:825
page_copy_sane.part.8+0x0/0x8
To avoid above warning, use __GFP_COMP while allocating multiple
contiguous pages.
Signed-off-by: Tushar Dave <tushar.n.d...@oracle.com>
---
net/core/filter.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index d301134..0b40f95 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2344,7 +2344,8 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
if (unlikely(bytes_sg_total > copy))
return -EINVAL;
- page = alloc_pages(__GFP_NOWARN | GFP_ATOMIC, get_order(copy));
+ page = alloc_pages(__GFP_NOWARN | GFP_ATOMIC | __GFP_COMP,
+ get_order(copy));
if (unlikely(!page))
return -ENOMEM;
p = page_address(page);
I should have mentioned that I could re-order this patch anywhere in
patch series (as long as it doesn't break git bisect). I kept it first
because I think it is more like a bug fix. I sent it along with these
patch series considering we have a context of why and for what I need
this patch!
Daniel, John,
Not sure if you guys hit this page_copy_sane warning. I hit it when RDS
copy sg page to userspace using copy_page_to_iter().
I have not hit this before but I'm working on a set of patches for
test_sockmap to test the bpf_msg_pull_data() so I'll add a case
for this. Currently, we only test the simple case where we pull
data out of a single page in selftests. This was sufficient for
my use case but missed a handful of other valid cases.
example:
RDS packet size 8KB represented in scatterlist:
sg_data[0].length = 1400
sg_data[1].length = 1448
sg_data[2].length = 1448
sg_data[3].length = 1448
sg_data[4].length = 1448
sg_data[5].length = 1000
If start=0 and end=8192, bpf_msg_pull_data() will linearize all
sg_data elements into one shared page. e.g. sg_data[0].length = 8192.
Using this sg_data[0].page in function copy_page_to_iter() causes:
WARNING: CPU: 2 PID: 7410 at lib/iov_iter.c:825
page_copy_sane.part.8+0x0/0x8
(FYI, patch 4 has code that does copy_page_to_iter)
How about sending it as a bugfix against bpf on its own. It
looks like we could reproduce this with a combination of
bpf_msg_pull_data() + redirect (to ingress) perhaps. Either
way seems like a candidate for the bpf fixes tree to me.
Done.
Thanks.
-Tushar
Thanks,
John
Comments?
Thanks in advance,
-Tushar
