Commit b261eda8 authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Paolo Abeni
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soreuseport: Fix socket selection for SO_INCOMING_CPU. 



Kazuho Oku reported that setsockopt(SO_INCOMING_CPU) does not work
with setsockopt(SO_REUSEPORT) since v4.6.

With the combination of SO_REUSEPORT and SO_INCOMING_CPU, we could
build a highly efficient server application.

setsockopt(SO_INCOMING_CPU) associates a CPU with a TCP listener
or UDP socket, and then incoming packets processed on the CPU will
likely be distributed to the socket.  Technically, a socket could
even receive packets handled on another CPU if no sockets in the
reuseport group have the same CPU receiving the flow.

The logic exists in compute_score() so that a socket will get a higher
score if it has the same CPU with the flow.  However, the score gets
ignored after the blamed two commits, which introduced a faster socket
selection algorithm for SO_REUSEPORT.

This patch introduces a counter of sockets with SO_INCOMING_CPU in
a reuseport group to check if we should iterate all sockets to find
a proper one.  We increment the counter when

  * calling listen() if the socket has SO_INCOMING_CPU and SO_REUSEPORT

  * enabling SO_INCOMING_CPU if the socket is in a reuseport group

Also, we decrement it when

  * detaching a socket out of the group to apply SO_INCOMING_CPU to
    migrated TCP requests

  * disabling SO_INCOMING_CPU if the socket is in a reuseport group

When the counter reaches 0, we can get back to the O(1) selection
algorithm.

The overall changes are negligible for the non-SO_INCOMING_CPU case,
and the only notable thing is that we have to update sk_incomnig_cpu
under reuseport_lock.  Otherwise, the race prevents transitioning to
the O(n) algorithm and results in the wrong socket selection.

 cpu1 (setsockopt)               cpu2 (listen)
+-----------------+             +-------------+

lock_sock(sk1)                  lock_sock(sk2)

reuseport_update_incoming_cpu(sk1, val)
.
|  /* set CPU as 0 */
|- WRITE_ONCE(sk1->incoming_cpu, val)
|
|                               spin_lock_bh(&reuseport_lock)
|                               reuseport_grow(sk2, reuse)
|                               .
|                               |- more_socks_size = reuse->max_socks * 2U;
|                               |- if (more_socks_size > U16_MAX &&
|                               |       reuse->num_closed_socks)
|                               |  .
|                               |  |- RCU_INIT_POINTER(sk1->sk_reuseport_cb, NULL);
|                               |  `- __reuseport_detach_closed_sock(sk1, reuse)
|                               |     .
|                               |     `- reuseport_put_incoming_cpu(sk1, reuse)
|                               |        .
|                               |        |  /* Read shutdown()ed sk1's sk_incoming_cpu
|                               |        |   * without lock_sock().
|                               |        |   */
|                               |        `- if (sk1->sk_incoming_cpu >= 0)
|                               |           .
|                               |           |  /* decrement not-yet-incremented
|                               |           |   * count, which is never incremented.
|                               |           |   */
|                               |           `- __reuseport_put_incoming_cpu(reuse);
|                               |
|                               `- spin_lock_bh(&reuseport_lock)
|
|- spin_lock_bh(&reuseport_lock)
|
|- reuse = rcu_dereference_protected(sk1->sk_reuseport_cb, ...)
|- if (!reuse)
|  .
|  |  /* Cannot increment reuse->incoming_cpu. */
|  `- goto out;
|
`- spin_unlock_bh(&reuseport_lock)

Fixes: e32ea7e7 ("soreuseport: fast reuseport UDP socket selection")
Fixes: c125e80b ("soreuseport: fast reuseport TCP socket selection")
Reported-by: default avatarKazuho Oku <kazuhooku@gmail.com>
Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent 71920a77

include/net/sock_reuseport.h

+2 −0
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ struct sock_reuseport { 
	u16			max_socks;		/* length of socks */

	u16			num_socks;		/* elements in socks */

	u16			num_closed_socks;	/* closed elements in socks */

	u16			incoming_cpu;

	/* The last synq overflow event timestamp of this

	 * reuse->socks[] group.

	 */
@@ -58,5 +59,6 @@ static inline bool reuseport_has_conns(struct sock *sk) 
}



void reuseport_has_conns_set(struct sock *sk);

void reuseport_update_incoming_cpu(struct sock *sk, int val);



#endif  /* _SOCK_REUSEPORT_H */

net/core/sock.c

+1 −1
Original line number Diff line number Diff line
@@ -1436,7 +1436,7 @@ int sk_setsockopt(struct sock *sk, int level, int optname, 
		break;

		}

	case SO_INCOMING_CPU:

		WRITE_ONCE(sk->sk_incoming_cpu, val);

		reuseport_update_incoming_cpu(sk, val);

		break;



	case SO_CNX_ADVICE:

net/core/sock_reuseport.c

+89 −5
Original line number Diff line number Diff line
@@ -37,6 +37,70 @@ void reuseport_has_conns_set(struct sock *sk) 
}

EXPORT_SYMBOL(reuseport_has_conns_set);



static void __reuseport_get_incoming_cpu(struct sock_reuseport *reuse)

{

	/* Paired with READ_ONCE() in reuseport_select_sock_by_hash(). */

	WRITE_ONCE(reuse->incoming_cpu, reuse->incoming_cpu + 1);

}



static void __reuseport_put_incoming_cpu(struct sock_reuseport *reuse)

{

	/* Paired with READ_ONCE() in reuseport_select_sock_by_hash(). */

	WRITE_ONCE(reuse->incoming_cpu, reuse->incoming_cpu - 1);

}



static void reuseport_get_incoming_cpu(struct sock *sk, struct sock_reuseport *reuse)

{

	if (sk->sk_incoming_cpu >= 0)

		__reuseport_get_incoming_cpu(reuse);

}



static void reuseport_put_incoming_cpu(struct sock *sk, struct sock_reuseport *reuse)

{

	if (sk->sk_incoming_cpu >= 0)

		__reuseport_put_incoming_cpu(reuse);

}



void reuseport_update_incoming_cpu(struct sock *sk, int val)

{

	struct sock_reuseport *reuse;

	int old_sk_incoming_cpu;



	if (unlikely(!rcu_access_pointer(sk->sk_reuseport_cb))) {

		/* Paired with REAE_ONCE() in sk_incoming_cpu_update()

		 * and compute_score().

		 */

		WRITE_ONCE(sk->sk_incoming_cpu, val);

		return;

	}



	spin_lock_bh(&reuseport_lock);



	/* This must be done under reuseport_lock to avoid a race with

	 * reuseport_grow(), which accesses sk->sk_incoming_cpu without

	 * lock_sock() when detaching a shutdown()ed sk.

	 *

	 * Paired with READ_ONCE() in reuseport_select_sock_by_hash().

	 */

	old_sk_incoming_cpu = sk->sk_incoming_cpu;

	WRITE_ONCE(sk->sk_incoming_cpu, val);



	reuse = rcu_dereference_protected(sk->sk_reuseport_cb,

					  lockdep_is_held(&reuseport_lock));



	/* reuseport_grow() has detached a closed sk. */

	if (!reuse)

		goto out;



	if (old_sk_incoming_cpu < 0 && val >= 0)

		__reuseport_get_incoming_cpu(reuse);

	else if (old_sk_incoming_cpu >= 0 && val < 0)

		__reuseport_put_incoming_cpu(reuse);



out:

	spin_unlock_bh(&reuseport_lock);

}



static int reuseport_sock_index(struct sock *sk,

				const struct sock_reuseport *reuse,

				bool closed)
@@ -64,6 +128,7 @@ static void __reuseport_add_sock(struct sock *sk, 
	/* paired with smp_rmb() in reuseport_(select|migrate)_sock() */

	smp_wmb();

	reuse->num_socks++;

	reuseport_get_incoming_cpu(sk, reuse);

}



static bool __reuseport_detach_sock(struct sock *sk,
@@ -76,6 +141,7 @@ static bool __reuseport_detach_sock(struct sock *sk, 


	reuse->socks[i] = reuse->socks[reuse->num_socks - 1];

	reuse->num_socks--;

	reuseport_put_incoming_cpu(sk, reuse);



	return true;

}
@@ -86,6 +152,7 @@ static void __reuseport_add_closed_sock(struct sock *sk, 
	reuse->socks[reuse->max_socks - reuse->num_closed_socks - 1] = sk;

	/* paired with READ_ONCE() in inet_csk_bind_conflict() */

	WRITE_ONCE(reuse->num_closed_socks, reuse->num_closed_socks + 1);

	reuseport_get_incoming_cpu(sk, reuse);

}



static bool __reuseport_detach_closed_sock(struct sock *sk,
@@ -99,6 +166,7 @@ static bool __reuseport_detach_closed_sock(struct sock *sk, 
	reuse->socks[i] = reuse->socks[reuse->max_socks - reuse->num_closed_socks];

	/* paired with READ_ONCE() in inet_csk_bind_conflict() */

	WRITE_ONCE(reuse->num_closed_socks, reuse->num_closed_socks - 1);

	reuseport_put_incoming_cpu(sk, reuse);



	return true;

}
@@ -166,6 +234,7 @@ int reuseport_alloc(struct sock *sk, bool bind_inany) 
	reuse->bind_inany = bind_inany;

	reuse->socks[0] = sk;

	reuse->num_socks = 1;

	reuseport_get_incoming_cpu(sk, reuse);

	rcu_assign_pointer(sk->sk_reuseport_cb, reuse);



out:
@@ -209,6 +278,7 @@ static struct sock_reuseport *reuseport_grow(struct sock_reuseport *reuse) 
	more_reuse->reuseport_id = reuse->reuseport_id;

	more_reuse->bind_inany = reuse->bind_inany;

	more_reuse->has_conns = reuse->has_conns;

	more_reuse->incoming_cpu = reuse->incoming_cpu;



	memcpy(more_reuse->socks, reuse->socks,

	       reuse->num_socks * sizeof(struct sock *));
@@ -458,18 +528,32 @@ static struct sock *run_bpf_filter(struct sock_reuseport *reuse, u16 socks, 
static struct sock *reuseport_select_sock_by_hash(struct sock_reuseport *reuse,

						  u32 hash, u16 num_socks)

{

	struct sock *first_valid_sk = NULL;

	int i, j;



	i = j = reciprocal_scale(hash, num_socks);

	while (reuse->socks[i]->sk_state == TCP_ESTABLISHED) {

	do {

		struct sock *sk = reuse->socks[i];



		if (sk->sk_state != TCP_ESTABLISHED) {

			/* Paired with WRITE_ONCE() in __reuseport_(get|put)_incoming_cpu(). */

			if (!READ_ONCE(reuse->incoming_cpu))

				return sk;



			/* Paired with WRITE_ONCE() in reuseport_update_incoming_cpu(). */

			if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())

				return sk;



			if (!first_valid_sk)

				first_valid_sk = sk;

		}



		i++;

		if (i >= num_socks)

			i = 0;

		if (i == j)

			return NULL;

	}

	} while (i != j);



	return reuse->socks[i];

	return first_valid_sk;

}



/**