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Merge branch 'rfs-lockless-annotate'

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Eric Dumazet says:

====================
rfs: annotate lockless accesses

rfs runs without locks held, so we should annotate
read and writes to shared variables.

It should prevent compilers forcing writes
in the following situation:

  if (var != val)
     var = val;

A compiler could indeed simply avoid the conditional:

    var = val;

This matters if var is shared between many cpus.

v2: aligns one closing bracket (Simon)
    adds Fixes: tags (Jakub)
====================

Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David S. Miller 2023-06-07 10:09:05 +01:00
commit e3144ff52f
3 changed files with 22 additions and 9 deletions
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7
include/linux/netdevice.h
View File

@ -768,8 +768,11 @@ static inline void rps_record_sock_flow(struct rps_sock_flow_table *table,
/* We only give a hint, preemption can change CPU under us */
val |= raw_smp_processor_id();
if (table->ents[index] != val)
table->ents[index] = val;
/* The following WRITE_ONCE() is paired with the READ_ONCE()
* here, and another one in get_rps_cpu().
*/
if (READ_ONCE(table->ents[index]) != val)
WRITE_ONCE(table->ents[index], val);
}
}

18
include/net/sock.h
View File

@ -1152,8 +1152,12 @@ 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
}
@ -1162,15 +1166,19 @@ 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
}

6
net/core/dev.c
View File

@ -4471,8 +4471,10 @@ static int get_rps_cpu(struct net_device *dev, struct sk_buff *skb,
u32 next_cpu;
u32 ident;
/* First check into global flow table if there is a match */
ident = sock_flow_table->ents[hash & sock_flow_table->mask];
/* First check into global flow table if there is a match.
* This READ_ONCE() pairs with WRITE_ONCE() from rps_record_sock_flow().
*/
ident = READ_ONCE(sock_flow_table->ents[hash & sock_flow_table->mask]);
if ((ident ^ hash) & ~rps_cpu_mask)
goto try_rps;