Re: [PATCH v4 2/2] net: memcg: late association of sock to memcg

[Shakeel Butt <shakeelb@google.com>]

On Thu, Mar 12, 2020 at 7:03 AM Qian Cai <cai@lca.pw> wrote:
>
> On Mon, 2020-03-09 at 22:16 -0700, Shakeel Butt wrote:
> > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > index a4db79b1b643..65a3b2565102 100644
> > --- a/net/ipv4/inet_connection_sock.c
> > +++ b/net/ipv4/inet_connection_sock.c
> > @@ -482,6 +482,26 @@ struct sock *inet_csk_accept(struct sock *sk, int flags, int *err, bool kern)
> >               }
> >               spin_unlock_bh(&queue->fastopenq.lock);
> >       }
> > +
> > +     if (mem_cgroup_sockets_enabled) {
> > +             int amt;
> > +
> > +             /* atomically get the memory usage, set and charge the
> > +              * sk->sk_memcg.
> > +              */
> > +             lock_sock(newsk);
>
> Here we have a deadlock,

It's a missing lockdep annotation. Eric already has a patch in
progress to fix this and another typo in the original patch.

>
> [  362.620977][ T4106] WARNING: possible recursive locking detected
> [  362.626983][ T4106] 5.6.0-rc5-next-20200312+ #5 Tainted: G             L
> [  362.633941][ T4106] --------------------------------------------
> [  362.639944][ T4106] sshd/4106 is trying to acquire lock:
> [  362.645251][ T4106] 7bff008a2eae6330 (sk_lock-AF_INET){+.+.}, at:
> inet_csk_accept+0x370/0x45c
> inet_csk_accept at net/ipv4/inet_connection_sock.c:497
> [  362.653791][ T4106]
> [  362.653791][ T4106] but task is already holding lock:
> [  362.661007][ T4106] c0ff008a2eae9430 (sk_lock-AF_INET){+.+.}, at:
> inet_csk_accept+0x48/0x45c
> inet_csk_accept at net/ipv4/inet_connection_sock.c:451
> [  362.669452][ T4106]
> [  362.669452][ T4106] other info that might help us debug this:
> [  362.677364][ T4106]  Possible unsafe locking scenario:
> [  362.677364][ T4106]
> [  362.684666][ T4106]        CPU0
> [  362.687801][ T4106]        ----
> [  362.690937][ T4106]   lock(sk_lock-AF_INET);
> [  362.695204][ T4106]   lock(sk_lock-AF_INET);
> [  362.699472][ T4106]
> [  362.699472][ T4106]  *** DEADLOCK ***
> [  362.699472][ T4106]
> [  362.707469][ T4106]  May be due to missing lock nesting notation
> [  362.707469][ T4106]
> [  362.715643][ T4106] 1 lock held by sshd/4106:
> [  362.719993][ T4106]  #0: c0ff008a2eae9430 (sk_lock-AF_INET){+.+.}, at:
> inet_csk_accept+0x48/0x45c
> [  362.728874][ T4106]
> [  362.728874][ T4106] stack backtrace:
> [  362.734622][ T4106] CPU: 22 PID: 4106 Comm: sshd Tainted:
> G             L    5.6.0-rc5-next-20200312+ #5
> [  362.744096][ T4106] Hardware name: HPE Apollo
> 70             /C01_APACHE_MB         , BIOS L50_5.13_1.11 06/18/2019
> [  362.754525][ T4106] Call trace:
> [  362.757667][ T4106]  dump_backtrace+0x0/0x2c8
> [  362.762022][ T4106]  show_stack+0x20/0x2c
> [  362.766032][ T4106]  dump_stack+0xe8/0x150
> [  362.770128][ T4106]  validate_chain+0x2f08/0x35e0
> [  362.774830][ T4106]  __lock_acquire+0x868/0xc2c
> [  362.779358][ T4106]  lock_acquire+0x320/0x360
> [  362.783715][ T4106]  lock_sock_nested+0x9c/0xd8
> [  362.788243][ T4106]  inet_csk_accept+0x370/0x45c
> [  362.792861][ T4106]  inet_accept+0x80/0x1cc
> [  362.797045][ T4106]  __sys_accept4_file+0x1b0/0x2bc
> [  362.801921][ T4106]  __arm64_sys_accept+0x74/0xc8
> [  362.806625][ T4106]  do_el0_svc+0x170/0x240
> [  362.810807][ T4106]  el0_sync_handler+0x150/0x250
> [  362.815509][ T4106]  el0_sync+0x164/0x180
>
>
> > +
> > +             /* The sk has not been accepted yet, no need to look at
> > +              * sk->sk_wmem_queued.
> > +              */
> > +             amt = sk_mem_pages(newsk->sk_forward_alloc +
> > +                                atomic_read(&sk->sk_rmem_alloc));
> > +             mem_cgroup_sk_alloc(newsk);
> > +             if (newsk->sk_memcg && amt)
> > +                     mem_cgroup_charge_skmem(newsk->sk_memcg, amt);
> > +
> > +             release_sock(newsk);
> > +     }
> >  out:
> >       release_sock(sk);
> >       if (req)