tcp: Remove redundant sk_unhashed() in inet_unhash().

tcp: Remove redundant sk_unhashed() in inet_unhash().

inet_unhash() checks sk_unhashed() twice at the entry and after locking
ehash/lhash bucket.

The former was somehow added redundantly by commit 4f9bf2a2f5aa ("tcp:
Don't acquire inet_listen_hashbucket::lock with disabled BH.").

inet_unhash() is called for the full socket from 4 places, and it is
always under lock_sock() or the socket is not yet published to other
threads:

  1. __sk_prot_rehash()
     -> called from inet_sk_reselect_saddr(), which has
        lockdep_sock_is_held()

  2. sk_common_release()
     -> called when inet_create() or inet6_create() fail, then the
        socket is not yet published

  3. tcp_set_state()
     -> calls tcp_call_bpf_2arg(), and tcp_call_bpf() has
        sock_owned_by_me()

  4. inet_ctl_sock_create()
     -> creates a kernel socket and unhashes it immediately, but TCP
        socket is not hashed in sock_create_kern() (only SOCK_RAW is)

So we do not need to check sk_unhashed() twice before/after ehash/lhash
lock in inet_unhash().

Let's remove the 2nd one.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20250919083706.1863217-4-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>