Re: [PATCH v4 bpf/net 2/6] sockmap: Annotate sk->sk_write_space() for UDP.

[Martin KaFai Lau <martin.lau@linux.dev>]

On 3/4/26 7:43 PM, Kuniyuki Iwashima wrote:
> On Wed, Mar 4, 2026 at 5:48 PM Jiayuan Chen <jiayuan.chen@linux.dev> wrote:
>>
>> On Sat, Feb 21, 2026 at 11:30:49PM +0800, Kuniyuki Iwashima wrote:
>>> UDP TX skb->destructor() is sock_wfree(), and UDP only
>>> holds lock_sock() for UDP_CORK / MSG_MORE sendmsg().
>>>
>>> Otherwise, sk->sk_write_space() is read locklessly.
>>>
>>> Let's use WRITE_ONCE() and READ_ONCE() for sk->sk_write_space().
>>>
>>> Fixes: 7b98cd42b049 ("bpf: sockmap: Add UDP support")
>>> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
>>> ---
>>> v3: Use WRITE_ONCE() in udp_bpf_update_proto()
>>> v2: Cache sk->sk_write_space in sock_wfree()
>>> ---
>>>   net/core/skmsg.c   | 2 +-
>>>   net/core/sock.c    | 8 ++++++--
>>>   net/ipv4/udp_bpf.c | 2 +-
>>>   3 files changed, 8 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
>>> index 75fa94217e1e..3d7eb2f4ac98 100644
>>> --- a/net/core/skmsg.c
>>> +++ b/net/core/skmsg.c
>>> @@ -1297,7 +1297,7 @@ void sk_psock_start_verdict(struct sock *sk, struct sk_psock *psock)
>>>
>>>        psock->saved_data_ready = sk->sk_data_ready;
>>>        WRITE_ONCE(sk->sk_data_ready, sk_psock_verdict_data_ready);
>>> -     sk->sk_write_space = sk_psock_write_space;
>>> +     WRITE_ONCE(sk->sk_write_space, sk_psock_write_space);
>>>   }
>>
>> I noticed that Patch 1 and 2 were submitted earlier and are on bpf tree.
>> Given that Eric's commit (which you reviewed) is now in net.git, these two patches
>> should probably be dropped in the next version, right? Just confirming.
> 
> I was thinking git can just handle them well, and even the
> patch 2 has a delta in sock_wfree().

At least for patch 1, I am not sure git can handle it well without human 
intervention because the sk_write_space is backward from Eric.

For the missing change in sock_wfree (?), it probably makes sense to 
create a separate patch on top of Eric's change and target net. My 
understanding is patch 3-6 can be on its own without patch 1+2.