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rfs: annotate lockless accesses to sk->sk_rxhash

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[ Upstream commit 1e5c647c3f6d4f8497dedcd226204e1880e0ffb3 ]

Add READ_ONCE()/WRITE_ONCE() on accesses to sk->sk_rxhash.

This also prevents a (smart ?) compiler to remove the condition in:

if (sk->sk_rxhash != newval)
	sk->sk_rxhash = newval;

We need the condition to avoid dirtying a shared cache line.

Fixes: fec5e652e5 ("rfs: Receive Flow Steering")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Eric Dumazet 2023-06-06 07:41:14 +00:00 committed by Greg Kroah-Hartman
parent a4c72805fd
commit 28ac3cf2ac
1 changed files with 13 additions and 5 deletions
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18
include/net/sock.h
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@ -997,8 +997,12 @@ static inline void sock_rps_record_flow(const struct sock *sk)
* OR an additional socket flag
* [1] : sk_state and sk_prot are in the same cache line.
*/
if (sk->sk_state == TCP_ESTABLISHED)
sock_rps_record_flow_hash(sk->sk_rxhash);
if (sk->sk_state == TCP_ESTABLISHED) {
/* This READ_ONCE() is paired with the WRITE_ONCE()
* from sock_rps_save_rxhash() and sock_rps_reset_rxhash().
*/
sock_rps_record_flow_hash(READ_ONCE(sk->sk_rxhash));
}
}
#endif
}
@ -1007,15 +1011,19 @@ static inline void sock_rps_save_rxhash(struct sock *sk,
const struct sk_buff *skb)
{
#ifdef CONFIG_RPS
if (unlikely(sk->sk_rxhash != skb->hash))
sk->sk_rxhash = skb->hash;
/* The following WRITE_ONCE() is paired with the READ_ONCE()
* here, and another one in sock_rps_record_flow().
*/
if (unlikely(READ_ONCE(sk->sk_rxhash) != skb->hash))
WRITE_ONCE(sk->sk_rxhash, skb->hash);
#endif
}
static inline void sock_rps_reset_rxhash(struct sock *sk)
{
#ifdef CONFIG_RPS
sk->sk_rxhash = 0;
/* Paired with READ_ONCE() in sock_rps_record_flow() */
WRITE_ONCE(sk->sk_rxhash, 0);
#endif
}