Re: [PATCH 0/6 v3] kvmalloc

From: Daniel Borkmann
Date: Thu Jan 26 2017 - 08:10:42 EST

On 01/26/2017 12:58 PM, Michal Hocko wrote:
On Thu 26-01-17 12:33:55, Daniel Borkmann wrote:
On 01/26/2017 11:08 AM, Michal Hocko wrote:
If you disagree I can drop the bpf part of course...

If we could consolidate these spots with kvmalloc() eventually, I'm
all for it. But even if __GFP_NORETRY is not covered down to all
possible paths, it kind of does have an effect already of saying
'don't try too hard', so would it be harmful to still keep that for
now? If it's not, I'd personally prefer to just leave it as is until
there's some form of support by kvmalloc() and friends.

Well, you can use kvmalloc(size, GFP_KERNEL|__GFP_NORETRY). It is not
disallowed. It is not _supported_ which means that if it doesn't work as
you expect you are on your own. Which is actually the situation right
now as well. But I still think that this is just not right thing to do.
Even though it might happen to work in some cases it gives a false
impression of a solution. So I would rather go with

Hmm. 'On my own' means, we could potentially BUG somewhere down the
vmalloc implementation, etc, presumably? So it might in-fact be
harmful to pass that, right?

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 8697f43cf93c..a6dc4d596f14 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -53,6 +53,11 @@ void bpf_register_map_type(struct bpf_map_type_list *tl)

void *bpf_map_area_alloc(size_t size)
+ /*
+ * FIXME: we would really like to not trigger the OOM killer and rather
+ * fail instead. This is not supported right now. Please nag MM people
+ * if these OOM start bothering people.
+ */

Ok, I know this is out of scope for this series, but since i) this
is _not_ the _only_ spot right now which has such a construct and ii)
I am already kind of nagging a bit ;), my question would be, what
would it take to start supporting it?

return kvzalloc(size, GFP_USER);