Re: [PATCH bpf] bpf, sockmap: fix lock inversion between stab->lock and sk_callback_lock

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 6/16/26 5:11 PM, Sechang Lim wrote:
> sock_map_update_common() and __sock_map_delete() hold stab->lock and call
> sock_map_unref() -> sock_map_del_link() under it. sock_map_del_link() takes
> sk_callback_lock for write to stop the strparser and verdict, giving the
> lock order stab->lock -> sk_callback_lock.
>
> The opposite order comes from an SK_SKB stream parser. On RX,
> sk_psock_strp_data_ready() holds sk_callback_lock for read while running
> the parser. The verdict redirects the skb to egress, where a sched_cls


The commit message is wrong. A verdict does not redirect to egress
synchronously — sk_psock_skb_redirect() only queues the skb and
schedule_delayed_work()s sk_psock_backlog, so egress runs in workqueue
context, not under sk_callback_lock.


> program calls bpf_map_delete_elem() on a sockmap, which takes stab->lock:
>
>    WARNING: possible circular locking dependency detected
>    7.1.0-rc6 Not tainted
>    ------------------------------------------------------
>    syz.9.8824 is trying to acquire lock:
>    (&stab->lock){+.-.}-{3:3}, at: __sock_map_delete net/core/sock_map.c:421
>    but task is already holding lock:
>    (clock-AF_INET){++.-}-{3:3}, at: sk_psock_strp_data_ready net/core/skmsg.c:1173
>
>    -> #1 (clock-AF_INET){++.-}-{3:3}:
>           _raw_write_lock_bh
>           sock_map_del_link net/core/sock_map.c:167
>           sock_map_unref net/core/sock_map.c:184
>           sock_map_update_common net/core/sock_map.c:509
>           sock_map_update_elem_sys net/core/sock_map.c:588
>           map_update_elem kernel/bpf/syscall.c:1805
>
>    -> #0 (&stab->lock){+.-.}-{3:3}:
>           _raw_spin_lock_bh
>           __sock_map_delete net/core/sock_map.c:421
>           sock_map_delete_elem net/core/sock_map.c:452
>           bpf_prog_06044d24140080b6
>           tcx_run net/core/dev.c:4451
>           sch_handle_egress net/core/dev.c:4541
>           __dev_queue_xmit net/core/dev.c:4808
>           ...
>           tcp_bpf_strp_read_sock net/ipv4/tcp_bpf.c:701


I guess it is an ACK. What is the actual purpose of a sched_cls program 
calling

sockmap delete on the TX path of an ACK? If there is no real use case 
for it, this is

just broken BPF usage, not a kernel bug worth this change.