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

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