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Date: Fri, 11 Jun 2021 07:33:39 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.co.jp>
To: <eric.dumazet@...il.com>
CC: <andrii@...nel.org>, <ast@...nel.org>, <benh@...zon.com>,
<bpf@...r.kernel.org>, <daniel@...earbox.net>,
<davem@...emloft.net>, <edumazet@...gle.com>, <kafai@...com>,
<kuba@...nel.org>, <kuni1840@...il.com>, <kuniyu@...zon.co.jp>,
<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [PATCH v7 bpf-next 02/11] tcp: Add num_closed_socks to struct sock_reuseport.
From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 10 Jun 2021 19:38:45 +0200
> On 5/21/21 8:20 PM, Kuniyuki Iwashima wrote:
> > As noted in the following commit, a closed listener has to hold the
> > reference to the reuseport group for socket migration. This patch adds a
> > field (num_closed_socks) to struct sock_reuseport to manage closed sockets
> > within the same reuseport group. Moreover, this and the following commits
> > introduce some helper functions to split socks[] into two sections and keep
> > TCP_LISTEN and TCP_CLOSE sockets in each section. Like a double-ended
> > queue, we will place TCP_LISTEN sockets from the front and TCP_CLOSE
> > sockets from the end.
> >
> > TCP_LISTEN----------> <-------TCP_CLOSE
> > +---+---+ --- +---+ --- +---+ --- +---+
> > | 0 | 1 | ... | i | ... | j | ... | k |
> > +---+---+ --- +---+ --- +---+ --- +---+
> >
> > i = num_socks - 1
> > j = max_socks - num_closed_socks
> > k = max_socks - 1
> >
> > This patch also extends reuseport_add_sock() and reuseport_grow() to
> > support num_closed_socks.
> >
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.co.jp>
> > Acked-by: Martin KaFai Lau <kafai@...com>
> > ---
> > include/net/sock_reuseport.h | 5 ++-
> > net/core/sock_reuseport.c | 76 +++++++++++++++++++++++++++---------
> > 2 files changed, 60 insertions(+), 21 deletions(-)
> >
> > diff --git a/include/net/sock_reuseport.h b/include/net/sock_reuseport.h
> > index 505f1e18e9bf..0e558ca7afbf 100644
> > --- a/include/net/sock_reuseport.h
> > +++ b/include/net/sock_reuseport.h
> > @@ -13,8 +13,9 @@ extern spinlock_t reuseport_lock;
> > struct sock_reuseport {
> > struct rcu_head rcu;
> >
> > - u16 max_socks; /* length of socks */
> > - u16 num_socks; /* elements in socks */
> > + u16 max_socks; /* length of socks */
> > + u16 num_socks; /* elements in socks */
> > + u16 num_closed_socks; /* closed elements in socks */
> > /* The last synq overflow event timestamp of this
> > * reuse->socks[] group.
> > */
> > diff --git a/net/core/sock_reuseport.c b/net/core/sock_reuseport.c
> > index b065f0a103ed..079bd1aca0e7 100644
> > --- a/net/core/sock_reuseport.c
> > +++ b/net/core/sock_reuseport.c
> > @@ -18,6 +18,49 @@ DEFINE_SPINLOCK(reuseport_lock);
> >
> > static DEFINE_IDA(reuseport_ida);
> >
> > +static int reuseport_sock_index(struct sock *sk,
> > + struct sock_reuseport *reuse,
> > + bool closed)
>
>
> const struct sock_reuseport *reuse
I will add const to reuse.
Don't I need to make sk const?
>
>
> > +{
> > + int left, right;
> > +
> > + if (!closed) {
> > + left = 0;
> > + right = reuse->num_socks;
> > + } else {
> > + left = reuse->max_socks - reuse->num_closed_socks;
> > + right = reuse->max_socks;
> > + }
>
>
>
> > +
> > + for (; left < right; left++)
> > + if (reuse->socks[left] == sk)
> > + return left;
>
>
> Is this even possible (to return -1) ?
>
> > + return -1;
Yes.
In the next patch, reuseport_detach_sock() tries to detach a sock from the
closed section first. So, if tcp_migrate_req is disabled, then -1 is
returned immediately because left == right.
===
if (!__reuseport_detach_closed_sock(sk, reuse))
__reuseport_detach_sock(sk, reuse);
===
> > +}
> > +
> > +static void __reuseport_add_sock(struct sock *sk,
> > + struct sock_reuseport *reuse)
> > +{
> > + reuse->socks[reuse->num_socks] = sk;
> > + /* paired with smp_rmb() in reuseport_select_sock() */
> > + smp_wmb();
> > + reuse->num_socks++;
> > +}
> > +
> > +static bool __reuseport_detach_sock(struct sock *sk,
> > + struct sock_reuseport *reuse)
> > +{
> > + int i = reuseport_sock_index(sk, reuse, false);
> > +
> > + if (i == -1)
> > + return false;
> > +
> > + reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
> > + reuse->num_socks--;
> > +
> > + return true;
> > +}
> > +
> > static struct sock_reuseport *__reuseport_alloc(unsigned int max_socks)
> > {
> > unsigned int size = sizeof(struct sock_reuseport) +
> > @@ -72,9 +115,8 @@ int reuseport_alloc(struct sock *sk, bool bind_inany)
> > }
> >
> > reuse->reuseport_id = id;
> > - reuse->socks[0] = sk;
> > - reuse->num_socks = 1;
> > reuse->bind_inany = bind_inany;
> > + __reuseport_add_sock(sk, reuse);
>
> Not sure why you changed this part, really no smp_wmb() is needed at this point ?
I have just reused the helper function, but exactly smp_wmb() is not
needed. I will keep here as is.
>
> > rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
> >
> > out:
> > @@ -98,6 +140,7 @@ static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse)
> > return NULL;
> >
> > more_reuse->num_socks = reuse->num_socks;
> > + more_reuse->num_closed_socks = reuse->num_closed_socks;
> > more_reuse->prog = reuse->prog;
> > more_reuse->reuseport_id = reuse->reuseport_id;
> > more_reuse->bind_inany = reuse->bind_inany;
> > @@ -105,9 +148,13 @@ static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse)
> >
> > memcpy(more_reuse->socks, reuse->socks,
> > reuse->num_socks * sizeof(struct sock *));
> > + memcpy(more_reuse->socks +
> > + (more_reuse->max_socks - more_reuse->num_closed_socks),
> > + reuse->socks + reuse->num_socks,
>
> The second memcpy() is to copy the closed sockets,
> they should start at reuse->socks + (reuse->max_socks - reuse->num_closed_socks) ?
num_socks == (reuse->max_socks - reuse->num_closed_socks) here, but I think
the latter is less error-prone so I will fix that.
Thank you.
>
>
> > + reuse->num_closed_socks * sizeof(struct sock *));
> > more_reuse->synq_overflow_ts = READ_ONCE(reuse->synq_overflow_ts);
> >
> > - for (i = 0; i < reuse->num_socks; ++i)
> > + for (i = 0; i < reuse->max_socks; ++i)
> > rcu_assign_pointer(reuse->socks[i]->sk_reuseport_cb,
> > more_reuse);
> >
> > @@ -158,7 +205,7 @@ int reuseport_add_sock(struct sock *sk, struct sock *sk2, bool bind_inany)
> > return -EBUSY;
> > }
> >
> > - if (reuse->num_socks == reuse->max_socks) {
> > + if (reuse->num_socks + reuse->num_closed_socks == reuse->max_socks) {
> > reuse = reuseport_grow(reuse);
> > if (!reuse) {
> > spin_unlock_bh(&reuseport_lock);
> > @@ -166,10 +213,7 @@ int reuseport_add_sock(struct sock *sk, struct sock *sk2, bool bind_inany)
> > }
> > }
> >
> > - reuse->socks[reuse->num_socks] = sk;
> > - /* paired with smp_rmb() in reuseport_select_sock() */
> > - smp_wmb();
> > - reuse->num_socks++;
> > + __reuseport_add_sock(sk, reuse);
> > rcu_assign_pointer(sk->sk_reuseport_cb, reuse);
> >
> > spin_unlock_bh(&reuseport_lock);
> > @@ -183,7 +227,6 @@ EXPORT_SYMBOL(reuseport_add_sock);
> > void reuseport_detach_sock(struct sock *sk)
> > {
> > struct sock_reuseport *reuse;
> > - int i;
> >
> > spin_lock_bh(&reuseport_lock);
> > reuse = rcu_dereference_protected(sk->sk_reuseport_cb,
> > @@ -200,16 +243,11 @@ void reuseport_detach_sock(struct sock *sk)
> > bpf_sk_reuseport_detach(sk);
> >
> > rcu_assign_pointer(sk->sk_reuseport_cb, NULL);
> > + __reuseport_detach_sock(sk, reuse);
> > +
> > + if (reuse->num_socks + reuse->num_closed_socks == 0)
> > + call_rcu(&reuse->rcu, reuseport_free_rcu);
> >
> > - for (i = 0; i < reuse->num_socks; i++) {
> > - if (reuse->socks[i] == sk) {
> > - reuse->socks[i] = reuse->socks[reuse->num_socks - 1];
> > - reuse->num_socks--;
> > - if (reuse->num_socks == 0)
> > - call_rcu(&reuse->rcu, reuseport_free_rcu);
> > - break;
> > - }
> > - }
> > spin_unlock_bh(&reuseport_lock);
> > }
> > EXPORT_SYMBOL(reuseport_detach_sock);
> > @@ -274,7 +312,7 @@ struct sock *reuseport_select_sock(struct sock *sk,
> > prog = rcu_dereference(reuse->prog);
> > socks = READ_ONCE(reuse->num_socks);
> > if (likely(socks)) {
> > - /* paired with smp_wmb() in reuseport_add_sock() */
> > + /* paired with smp_wmb() in __reuseport_add_sock() */
> > smp_rmb();
> >
> > if (!prog || !skb)
> >
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