From: Martin KaFai Lau <ka...@fb.com> Date: Wed, 18 Nov 2020 17:00:45 -0800 > On Tue, Nov 17, 2020 at 06:40:22PM +0900, Kuniyuki Iwashima wrote: > > This patch makes it possible to select a new listener for socket migration > > by eBPF. > > > > The noteworthy point is that we select a listening socket in > > reuseport_detach_sock() and reuseport_select_sock(), but we do not have > > struct skb in the unhash path. > > > > Since we cannot pass skb to the eBPF program, we run only the > > BPF_PROG_TYPE_SK_REUSEPORT program by calling bpf_run_sk_reuseport() with > > skb NULL. So, some fields derived from skb are also NULL in the eBPF > > program. > More things need to be considered here when skb is NULL. > > Some helpers are probably assuming skb is not NULL. > > Also, the sk_lookup in filter.c is actually passing a NULL skb to avoid > doing the reuseport select.
Honestly, I have missed this point... I wanted users to reuse the same eBPF program seamlessly, but it seems unsafe. > > Moreover, we can cancel migration by returning SK_DROP. This feature is > > useful when listeners have different settings at the socket API level or > > when we want to free resources as soon as possible. > > > > Reviewed-by: Benjamin Herrenschmidt <b...@amazon.com> > > Signed-off-by: Kuniyuki Iwashima <kun...@amazon.co.jp> > > --- > > net/core/filter.c | 26 +++++++++++++++++++++----- > > net/core/sock_reuseport.c | 23 ++++++++++++++++++++--- > > net/ipv4/inet_hashtables.c | 2 +- > > 3 files changed, 42 insertions(+), 9 deletions(-) > > > > diff --git a/net/core/filter.c b/net/core/filter.c > > index 01e28f283962..ffc4591878b8 100644 > > --- a/net/core/filter.c > > +++ b/net/core/filter.c > > @@ -8914,6 +8914,22 @@ static u32 xdp_convert_ctx_access(enum > > bpf_access_type type, > > SOCK_ADDR_LOAD_NESTED_FIELD_SIZE_OFF(S, NS, F, NF, \ > > BPF_FIELD_SIZEOF(NS, NF), 0) > > > > +#define SOCK_ADDR_LOAD_NESTED_FIELD_SIZE_OFF_OR_NULL(S, NS, F, NF, SIZE, > > OFF) \ > > + do { > > \ > > + *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(S, F), si->dst_reg, > > \ > > + si->src_reg, offsetof(S, F)); > > \ > > + *insn++ = BPF_JMP_IMM(BPF_JEQ, si->dst_reg, 0, 1); > > \ > Although it may not matter much, always doing this check seems not very ideal > considering the fast path will always have skb and only the slow > path (accept-queue migrate) has skb is NULL. I think the req_sk usually > has the skb also except the timer one. Yes, but the migration happens only when/after the listener is closed, so I think it does not occur so frequently and will not be a problem. > First thought is to create a temp skb but it has its own issues. > or it may actually belong to a new prog type. However, lets keep > exploring possible options (including NULL skb). I also thought up the two ideas, but the former will be a bit complicated. And the latter makes users implement the new eBPF program. I did not want users to struggle anymore, so I have selected the NULL skb. However, it is not safe, so adding a new prog type seems to be the better way.