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rfs: annotate lockless accesses to RFS sock flow table

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Add READ_ONCE()/WRITE_ONCE() on accesses to the sock flow table.

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

if (table->ents[index] != newval)
        table->ents[index] = newval;

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

Fixes: fec5e652e58f ("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>
This commit is contained in:
Eric Dumazet 2023-06-06 07:41:15 +00:00 committed by David S. Miller
parent 1e5c647c3f
commit 5c3b74a92a
2 changed files with 9 additions and 4 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);
}
}

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;