From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ 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: fec5e652e58f ("rfs: Receive Flow Steering")
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Simon Horman <simon.horman@xxxxxxxxxxxx>
Reviewed-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/net/sock.h | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)
diff --git a/include/net/sock.h b/include/net/sock.h
index ee1a2217a98c0..eccec5df94b9c 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -957,8 +957,12 @@ 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
}
@@ -967,15 +971,19 @@ 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
}
--
2.39.2
