linux-kernel - Re: [PATCH 1/8] af_unix: take address assignment/hash insertion into a new helper

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Message-ID: <CAM_iQpXX7SBGgUkBUY6BEjCqJYbHAUW5Z3VtV2U=yhiw1YJr=w@mail.gmail.com>
Date:   Sat, 20 Feb 2021 12:31:49 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Denis Kirjanov <kda@...ux-powerpc.org>,
        Christoph Hellwig <hch@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 1/8] af_unix: take address assignment/hash insertion into
 a new helper

On Sat, Feb 20, 2021 at 11:32 AM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Sat, Feb 20, 2021 at 11:12:33AM -0800, Cong Wang wrote:
> > On Thu, Feb 18, 2021 at 8:22 PM Al Viro <viro@...iv.linux.org.uk> wrote:
> > >
> > > Duplicated logics in all bind variants (autobind, bind-to-path,
> > > bind-to-abstract) gets taken into a common helper.
> > >
> > > Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
> > > ---
> > >  net/unix/af_unix.c | 30 +++++++++++++++---------------
> > >  1 file changed, 15 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > > index 41c3303c3357..179b4fe837e6 100644
> > > --- a/net/unix/af_unix.c
> > > +++ b/net/unix/af_unix.c
> > > @@ -262,6 +262,16 @@ static void __unix_insert_socket(struct hlist_head *list, struct sock *sk)
> > >         sk_add_node(sk, list);
> > >  }
> > >
> > > +static void __unix_set_addr(struct sock *sk, struct unix_address *addr,
> > > +                           unsigned hash)
> > > +       __releases(&unix_table_lock)
> > > +{
> > > +       __unix_remove_socket(sk);
> > > +       smp_store_release(&unix_sk(sk)->addr, addr);
> > > +       __unix_insert_socket(&unix_socket_table[hash], sk);
> > > +       spin_unlock(&unix_table_lock);
> >
> > Please take the unlock out, it is clearly an anti-pattern.
>
> Why?  "Insert into locked and unlock" is fairly common...

Because it does not lock the lock, just compare:

lock();
__unix_set_addr();
unlock();

to:

lock();
__unix_set_addr();

Clearly the former is more readable and less error-prone. Even
if you really want to do unlock, pick a name which explicitly says
it, for example, __unix_set_addr_unlock().

Thanks.