Re: [patch net-next 1/2] team: use rcu_access_pointer to access RCU pointer by writer

Wed, Jun 20, 2012 at 06:01:44PM CEST, eric.dumazet@gmail.com wrote:

On Wed, 2012-06-20 at 17:32 +0200, Jiri Pirko wrote:

quoted

Signed-off-by: Jiri Pirko <redacted>
---
 drivers/net/team/team_mode_activebackup.c |    7 +++++--
 drivers/net/team/team_mode_loadbalance.c  |    8 +++++---
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/net/team/team_mode_activebackup.c b/drivers/net/team/team_mode_activebackup.c
index 2fe02a8..c9e7621 100644
--- a/drivers/net/team/team_mode_activebackup.c
+++ b/drivers/net/team/team_mode_activebackup.c

@@ -61,8 +61,11 @@ static void ab_port_leave(struct team *team, struct team_port *port)
 
 static int ab_active_port_get(struct team *team, struct team_gsetter_ctx *ctx)
 {
-	if (ab_priv(team)->active_port)
-		ctx->data.u32_val = ab_priv(team)->active_port->dev->ifindex;
+	struct team_port *active_port;
+
+	active_port = rcu_access_pointer(ab_priv(team)->active_port);

This is not the correct fix.

You cant safely dereference active_port if you got it from
rcu_access_pointer()

You should use rcu_dereference() of rcu_dereference_protected() or
rcu_dereference_bh() or similar variant, depending on the context.

Okay, reworking this using rcu_dereference_protected() since this is
update path.

quoted

+	if (active_port)
+		ctx->data.u32_val = active_port->dev->ifindex;
 	else
 		ctx->data.u32_val = 0;
 	return 0;

diff --git a/drivers/net/team/team_mode_loadbalance.c b/drivers/net/team/team_mode_loadbalance.c
index 45cc095..b4475a5 100644
--- a/drivers/net/team/team_mode_loadbalance.c
+++ b/drivers/net/team/team_mode_loadbalance.c

@@ -96,7 +96,7 @@ static void lb_tx_hash_to_port_mapping_null_port(struct team *team,
 		struct lb_port_mapping *pm;
 
 		pm = &lb_priv->ex->tx_hash_to_port_mapping[i];
-		if (pm->port == port) {
+		if (rcu_access_pointer(pm->port) == port) {

This one is OK

quoted

 			rcu_assign_pointer(pm->port, NULL);

I dont understand why you submit two patches...

Squashing into one now.

quoted

 			team_option_inst_set_change(pm->opt_inst_info);
 			changed = true;

@@ -292,7 +292,7 @@ static int lb_bpf_func_set(struct team *team, struct team_gsetter_ctx *ctx)
 	if (lb_priv->ex->orig_fprog) {
 		/* Clear old filter data */
 		__fprog_destroy(lb_priv->ex->orig_fprog);
-		sk_unattached_filter_destroy(lb_priv->fp);
+		sk_unattached_filter_destroy(rcu_access_pointer(lb_priv->fp));
 	}