Merge branch 'rfs-lockless-annotate'

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>

1 files changed, 5 insertions, 2 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 08fbd4622ccf..e6f22b7403d0 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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);
 	}
 }