[PATCH] net: bonding: Fix transmit load balancing in balance-alb mode if specified by sysfs

[Kosuke Tatsukawa]

Commit cbf5ecb30560 ("net: bonding: Fix transmit load balancing in
balance-alb mode") tried to fix transmit dynamic load balancing in
balance-alb mode, which wasn't working after commit 8b426dc54cf4
("bonding: remove hardcoded value").

It turned out that my previous patch only fixed the case when
balance-alb was specified as bonding module parameter, and not when
balance-alb mode was set using /sys/class/net/*/bonding/mode (the most
common usage).  In the latter case, tlb_dynamic_lb was set up according
to the default mode of the bonding interface, which happens to be
balance-rr.

This additional patch addresses this issue by setting up tlb_dynamic_lb
to 1 if "mode" is set to balance-alb through the sysfs interface.

I didn't add code to change tlb_balance_lb back to the default value for
other modes, because "mode" is usually set up only once during
initialization, and it's not worthwhile to change the static variable
bonding_defaults in bond_main.c to a global variable just for this
purpose.

Commit 8b426dc54cf4 also changes the value of tlb_dynamic_lb for
balance-tlb mode if it is set up using the sysfs interface.  I didn't
change that behavior, because the value of tlb_balance_lb can be changed
using the sysfs interface for balance-tlb, and I didn't like changing
the default value back and forth for balance-tlb.

As for balance-alb, /sys/class/net/*/bonding/tlb_balance_lb cannot be
written to.  However, I think balance-alb with tlb_dynamic_lb set to 0
is not an intended usage, so there is little use making it writable at
this moment.

Fixes: 8b426dc54cf4 ("bonding: remove hardcoded value")
Reported-by: Reinis Rozitis <r@xxxxxxx>
Signed-off-by: Kosuke Tatsukawa <tatsu@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx  # v4.12+
---
 drivers/net/bonding/bond_options.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
index a12d603..5931aa2 100644
--- a/drivers/net/bonding/bond_options.c
+++ b/drivers/net/bonding/bond_options.c
@@ -754,6 +754,9 @@ static int bond_option_mode_set(struct bonding *bond,
 			   bond->params.miimon);
 	}
 
+	if (newval->value == BOND_MODE_ALB)
+		bond->params.tlb_dynamic_lb = 1;
+
 	/* don't cache arp_validate between modes */
 	bond->params.arp_validate = BOND_ARP_VALIDATE_NONE;
 	bond->params.mode = newval->value;