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Date: Tue, 14 Jun 2022 11:08:41 -0700
From: Joanne Koong <joannelkoong@...il.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Mat Martineau <mathew.j.martineau@...ux.intel.com>,
netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Martin KaFai Lau <kafai@...com>,
Jakub Kicinski <kuba@...nel.org>,
David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next v3 2/3] net: Add bhash2 hashbucket locks
On Tue, Jun 14, 2022 at 7:12 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On Mon, 2022-06-13 at 15:12 -0700, Mat Martineau wrote:
> > On Fri, 10 Jun 2022, Joanne Koong wrote:
> >
> > > Currently, the bhash2 hashbucket uses its corresponding bhash
> > > hashbucket's lock for serializing concurrent accesses. There,
> > > however, can be the case where the bhash2 hashbucket is accessed
> > > concurrently by multiple processes that hash to different bhash
> > > hashbuckets but to the same bhash2 hashbucket.
> > >
> > > As such, each bhash2 hashbucket will need to have its own lock
> > > instead of using its corresponding bhash hashbucket's lock.
> > >
> > > Fixes: d5a42de8bdbe ("net: Add a second bind table hashed by port and address")
> > > Signed-off-by: Joanne Koong <joannelkoong@...il.com>
> > > ---
> > > include/net/inet_hashtables.h | 25 +++----
> > > net/dccp/proto.c | 3 +-
> > > net/ipv4/inet_connection_sock.c | 60 +++++++++-------
> > > net/ipv4/inet_hashtables.c | 119 +++++++++++++++-----------------
> > > net/ipv4/tcp.c | 7 +-
> > > 5 files changed, 107 insertions(+), 107 deletions(-)
> > >
> > > diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
> > > index 2c331ce6ca73..c5b112f0938b 100644
> > > --- a/include/net/inet_hashtables.h
> > > +++ b/include/net/inet_hashtables.h
> > > @@ -124,15 +124,6 @@ struct inet_bind_hashbucket {
> > > struct hlist_head chain;
> > > };
> > >
> > > -/* This is synchronized using the inet_bind_hashbucket's spinlock.
> > > - * Instead of having separate spinlocks, the inet_bind2_hashbucket can share
> > > - * the inet_bind_hashbucket's given that in every case where the bhash2 table
> > > - * is useful, a lookup in the bhash table also occurs.
> > > - */
> > > -struct inet_bind2_hashbucket {
> > > - struct hlist_head chain;
> > > -};
> > > -
> > > /* Sockets can be hashed in established or listening table.
> > > * We must use different 'nulls' end-of-chain value for all hash buckets :
> > > * A socket might transition from ESTABLISH to LISTEN state without
> > > @@ -169,7 +160,7 @@ struct inet_hashinfo {
> > > * conflicts.
> > > */
> > > struct kmem_cache *bind2_bucket_cachep;
> > > - struct inet_bind2_hashbucket *bhash2;
> > > + struct inet_bind_hashbucket *bhash2;
> > > unsigned int bhash_size;
> > >
> > > /* The 2nd listener table hashed by local port and address */
> > > @@ -240,7 +231,7 @@ static inline bool check_bind_bucket_match(struct inet_bind_bucket *tb,
> > >
> > > struct inet_bind2_bucket *
> > > inet_bind2_bucket_create(struct kmem_cache *cachep, struct net *net,
> > > - struct inet_bind2_hashbucket *head,
> > > + struct inet_bind_hashbucket *head,
> > > const unsigned short port, int l3mdev,
> > > const struct sock *sk);
> > >
> > > @@ -248,12 +239,12 @@ void inet_bind2_bucket_destroy(struct kmem_cache *cachep,
> > > struct inet_bind2_bucket *tb);
> > >
> > > struct inet_bind2_bucket *
> > > -inet_bind2_bucket_find(struct inet_hashinfo *hinfo, struct net *net,
> > > +inet_bind2_bucket_find(struct inet_bind_hashbucket *head,
> > > + struct inet_hashinfo *hinfo, struct net *net,
> > > const unsigned short port, int l3mdev,
> > > - struct sock *sk,
> > > - struct inet_bind2_hashbucket **head);
> > > + struct sock *sk);
> > >
> > > -bool check_bind2_bucket_match_nulladdr(struct inet_bind2_bucket *tb,
> > > +bool check_bind2_bucket_match_addr_any(struct inet_bind2_bucket *tb,
> > > struct net *net,
> > > const unsigned short port,
> > > int l3mdev,
> > > @@ -265,6 +256,10 @@ static inline u32 inet_bhashfn(const struct net *net, const __u16 lport,
> > > return (lport + net_hash_mix(net)) & (bhash_size - 1);
> > > }
> > >
> > > +struct inet_bind_hashbucket *
> > > +inet_bhashfn_portaddr(struct inet_hashinfo *hinfo, const struct sock *sk,
> > > + const struct net *net, unsigned short port);
> > > +
> > > void inet_bind_hash(struct sock *sk, struct inet_bind_bucket *tb,
> > > struct inet_bind2_bucket *tb2, const unsigned short snum);
> > >
> > > diff --git a/net/dccp/proto.c b/net/dccp/proto.c
> > > index 2e78458900f2..f4f2ad5f9c08 100644
> > > --- a/net/dccp/proto.c
> > > +++ b/net/dccp/proto.c
> > > @@ -1182,7 +1182,7 @@ static int __init dccp_init(void)
> > > goto out_free_dccp_locks;
> > > }
> > >
> > > - dccp_hashinfo.bhash2 = (struct inet_bind2_hashbucket *)
> > > + dccp_hashinfo.bhash2 = (struct inet_bind_hashbucket *)
> > > __get_free_pages(GFP_ATOMIC | __GFP_NOWARN, bhash_order);
> > >
> > > if (!dccp_hashinfo.bhash2) {
> > > @@ -1193,6 +1193,7 @@ static int __init dccp_init(void)
> > > for (i = 0; i < dccp_hashinfo.bhash_size; i++) {
> > > spin_lock_init(&dccp_hashinfo.bhash[i].lock);
> > > INIT_HLIST_HEAD(&dccp_hashinfo.bhash[i].chain);
> > > + spin_lock_init(&dccp_hashinfo.bhash2[i].lock);
> > > INIT_HLIST_HEAD(&dccp_hashinfo.bhash2[i].chain);
> > > }
> > >
> > > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> > > index c0b7e6c21360..24a42e4d8234 100644
> > > --- a/net/ipv4/inet_connection_sock.c
> > > +++ b/net/ipv4/inet_connection_sock.c
> > > @@ -131,14 +131,14 @@ static bool use_bhash2_on_bind(const struct sock *sk)
> > > return sk->sk_rcv_saddr != htonl(INADDR_ANY);
> > > }
> > >
> > > -static u32 get_bhash2_nulladdr_hash(const struct sock *sk, struct net *net,
> > > +static u32 get_bhash2_addr_any_hash(const struct sock *sk, struct net *net,
> > > int port)
> > > {
> > > #if IS_ENABLED(CONFIG_IPV6)
> > > - struct in6_addr nulladdr = {};
> > > + struct in6_addr addr_any = {};
> > >
> > > if (sk->sk_family == AF_INET6)
> > > - return ipv6_portaddr_hash(net, &nulladdr, port);
> > > + return ipv6_portaddr_hash(net, &addr_any, port);
> > > #endif
> > > return ipv4_portaddr_hash(net, 0, port);
> > > }
> > > @@ -204,18 +204,18 @@ static bool check_bhash2_conflict(const struct sock *sk,
> > > return false;
> > > }
> > >
> > > -/* This should be called only when the corresponding inet_bind_bucket spinlock
> > > - * is held
> > > - */
> > > +/* This should be called only when the tb and tb2 hashbuckets' locks are held */
> > > static int inet_csk_bind_conflict(const struct sock *sk, int port,
> > > struct inet_bind_bucket *tb,
> > > struct inet_bind2_bucket *tb2, /* may be null */
> > > + struct inet_bind_hashbucket *head_tb2,
> > > bool relax, bool reuseport_ok)
> > > {
> > > struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
> > > kuid_t uid = sock_i_uid((struct sock *)sk);
> > > struct sock_reuseport *reuseport_cb;
> > > - struct inet_bind2_hashbucket *head2;
> > > + struct inet_bind_hashbucket *head_addr_any;
> > > + bool addr_any_conflict = false;
> > > bool reuseport_cb_ok;
> > > struct sock *sk2;
> > > struct net *net;
> > > @@ -254,33 +254,39 @@ static int inet_csk_bind_conflict(const struct sock *sk, int port,
> > > /* check there's no conflict with an existing IPV6_ADDR_ANY (if ipv6) or
> > > * INADDR_ANY (if ipv4) socket.
> > > */
> > > - hash = get_bhash2_nulladdr_hash(sk, net, port);
> > > - head2 = &hinfo->bhash2[hash & (hinfo->bhash_size - 1)];
> > > + hash = get_bhash2_addr_any_hash(sk, net, port);
> > > + head_addr_any = &hinfo->bhash2[hash & (hinfo->bhash_size - 1)];
> > >
> > > l3mdev = inet_sk_bound_l3mdev(sk);
> > > - inet_bind_bucket_for_each(tb2, &head2->chain)
> > > - if (check_bind2_bucket_match_nulladdr(tb2, net, port, l3mdev, sk))
> > > +
> > > + if (head_addr_any != head_tb2)
> > > + spin_lock_bh(&head_addr_any->lock);
> >
> > Hi Joanne -
> >
> > syzkaller is consistently hitting a warning here (about 10x per minute):
> >
> > ============================================
> > WARNING: possible recursive locking detected
> > 5.19.0-rc1-00382-g78347e8e15bf #1 Not tainted
> > --------------------------------------------
> > sshd/352 is trying to acquire lock:
> > ffffc90000968640 (&tcp_hashinfo.bhash2[i].lock){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:354 [inline]
> > ffffc90000968640 (&tcp_hashinfo.bhash2[i].lock){+.-.}-{2:2}, at: inet_csk_bind_conflict+0x4c4/0x8e0 net/ipv4/inet_connection_sock.c:263
> >
> > but task is already holding lock:
> > ffffc90000883d28 (&tcp_hashinfo.bhash2[i].lock){+.-.}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:354 [inline]
> > ffffc90000883d28 (&tcp_hashinfo.bhash2[i].lock){+.-.}-{2:2}, at: inet_csk_get_port+0x528/0xea0 net/ipv4/inet_connection_sock.c:497
> >
> > other info that might help us debug this:
> > Possible unsafe locking scenario:
> >
> > CPU0
> > ----
> > lock(&tcp_hashinfo.bhash2[i].lock);
> > lock(&tcp_hashinfo.bhash2[i].lock);
> >
> > *** DEADLOCK ***
> >
> > May be due to missing lock nesting notation
>
> This looks like a real deadlock scenario.
>
> One dumb way of solving it would be always acquiring the bhash2 lock
> for head_addr_any and for port/addr, in a fixed order - e.g. lower hash
> first.
>
> Anyway this fix looks not trivial. I'm wondering if we should consider
> a revert of the feature until a better/more robust design is ready?
>
Thanks for your feedback, Eric, Kuniyuki, Mat, and Paolo.
I think it's a good idea to revert bhash2 and then I will resubmit
once all the fixes are in place. Please let me know if there's
anything I need to do on my side to revert this.
Sorry for the inconveniences.
> Thanks
>
> Paolo
>
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