From: Eric Dumazet edumazet@google.com
[ Upstream commit 5c3b74a92aa285a3df722bf6329ba7ccf70346d6 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/netdevice.h | 7 +++++-- net/core/dev.c | 6 ++++-- 2 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 5b6c38f748076..823f5ed4ec0cc 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -737,8 +737,11 @@ 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); } }
diff --git a/net/core/dev.c b/net/core/dev.c index 56a3bff7249d4..24d711fe376a3 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -4458,8 +4458,10 @@ 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;