Subject: Re: [PATCH net v2] bonding: fix feature flag setting at init time

From: Jay Vosburgh <[email-masked]>
Date: Wed, 02 Dec 2020 09:55:28 -0800

Jarod Wilson <[email-masked]> wrote:

>Don't try to adjust XFRM support flags if the bond device isn't yet
>registered. Bad things can currently happen when netdev_change_features()
>is called without having wanted_features fully filled in yet. Basically,
>this code was racing against register_netdevice() filling in
>wanted_features, and when it got there first, the empty wanted_features
>led to features also getting emptied out, which was definitely not the
>intended behavior, so prevent that from happening.

	Is this an actual race?  Reading Ivan's prior message, it sounds
like it's an ordering problem (in that bond_newlink calls
register_netdevice after bond_changelink).

	The change to bond_option_mode_set tests against reg_state, so
presumably it wants to skip the first(?) time through, before the
register_netdevice call; is that right?

	-J

>Originally, I'd hoped to stop adjusting wanted_features at all in the
>bonding driver, as it's documented as being something only the network
>core should touch, but we actually do need to do this to properly update
>both the features and wanted_features fields when changing the bond type,
>or we get to a situation where ethtool sees:
>
>    esp-hw-offload: off [requested on]
>
>I do think we should be using netdev_update_features instead of
>netdev_change_features here though, so we only send notifiers when the
>features actually changed.
>
>v2: rework based on further testing and suggestions from ivecera
>
>Fixes: a3b658cfb664 ("bonding: allow xfrm offload setup post-module-load")
>Reported-by: Ivan Vecera <[email-masked]>
>Suggested-by: Ivan Vecera <[email-masked]>
>Cc: Jay Vosburgh <[email-masked]>
>Cc: Veaceslav Falico <[email-masked]>
>Cc: Andy Gospodarek <[email-masked]>
>Cc: "David S. Miller" <[email-masked]>
>Cc: Jakub Kicinski <[email-masked]>
>Cc: Thomas Davis <[email-masked]>
>Cc: [email-masked]
>Signed-off-by: Jarod Wilson <[email-masked]>
>---
> drivers/net/bonding/bond_main.c    | 10 ++++------
> drivers/net/bonding/bond_options.c |  6 +++++-
> 2 files changed, 9 insertions(+), 7 deletions(-)
>
>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>index e0880a3840d7..5fe5232cc3f3 100644
>--- a/drivers/net/bonding/bond_main.c
>+++ b/drivers/net/bonding/bond_main.c
>@@ -4746,15 +4746,13 @@ void bond_setup(struct net_device *bond_dev)
> 				NETIF_F_HW_VLAN_CTAG_FILTER;
> 
> 	bond_dev->hw_features |= NETIF_F_GSO_ENCAP_ALL;
>-#ifdef CONFIG_XFRM_OFFLOAD
>-	bond_dev->hw_features |= BOND_XFRM_FEATURES;
>-#endif /* CONFIG_XFRM_OFFLOAD */
> 	bond_dev->features |= bond_dev->hw_features;
> 	bond_dev->features |= NETIF_F_HW_VLAN_CTAG_TX | NETIF_F_HW_VLAN_STAG_TX;
> #ifdef CONFIG_XFRM_OFFLOAD
>-	/* Disable XFRM features if this isn't an active-backup config */
>-	if (BOND_MODE(bond) != BOND_MODE_ACTIVEBACKUP)
>-		bond_dev->features &= ~BOND_XFRM_FEATURES;
>+	bond_dev->hw_features |= BOND_XFRM_FEATURES;
>+	/* Only enable XFRM features if this is an active-backup config */
>+	if (BOND_MODE(bond) == BOND_MODE_ACTIVEBACKUP)
>+		bond_dev->features |= BOND_XFRM_FEATURES;
> #endif /* CONFIG_XFRM_OFFLOAD */
> }
> 
>diff --git a/drivers/net/bonding/bond_options.c b/drivers/net/bonding/bond_options.c
>index 9abfaae1c6f7..19205cfac751 100644
>--- a/drivers/net/bonding/bond_options.c
>+++ b/drivers/net/bonding/bond_options.c
>@@ -768,11 +768,15 @@ static int bond_option_mode_set(struct bonding *bond,
> 		bond->params.tlb_dynamic_lb = 1;
> 
> #ifdef CONFIG_XFRM_OFFLOAD
>+	if (bond->dev->reg_state != NETREG_REGISTERED)
>+		goto noreg;
>+
> 	if (newval->value == BOND_MODE_ACTIVEBACKUP)
> 		bond->dev->wanted_features |= BOND_XFRM_FEATURES;
> 	else
> 		bond->dev->wanted_features &= ~BOND_XFRM_FEATURES;
>-	netdev_change_features(bond->dev);
>+	netdev_update_features(bond->dev);
>+noreg:
>
> #endif /* CONFIG_XFRM_OFFLOAD */
> 
> 	/* don't cache arp_validate between modes */
>-- 
>2.28.0
>

---
	-Jay Vosburgh, [email-masked]