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authorKuniyuki Iwashima <kuniyu@amazon.com>2022-10-21 13:44:34 -0700
committerPaolo Abeni <pabeni@redhat.com>2022-10-25 11:35:16 +0200
commitb261eda84ec136240a9ca753389853a3a1bccca2 (patch)
treec72d1df66bca01deed03cdcc87dba0b9f2170e76 /net/core/sock.c
parent71920a773e522b6a34bba957a3aacc99cefa3836 (diff)
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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: e32ea7e74727 ("soreuseport: fast reuseport UDP socket selection") Fixes: c125e80b8868 ("soreuseport: fast reuseport TCP socket selection") Reported-by: Kazuho Oku <kazuhooku@gmail.com> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'net/core/sock.c')
-rw-r--r--net/core/sock.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/net/core/sock.c b/net/core/sock.c
index 2786c1107e53..4571914a4aa8 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1436,7 +1436,7 @@ set_sndbuf:
break;
}
case SO_INCOMING_CPU:
- WRITE_ONCE(sk->sk_incoming_cpu, val);
+ reuseport_update_incoming_cpu(sk, val);
break;
case SO_CNX_ADVICE: