Subject: Re: [PATCH net-next,v3] bonding: use WARN_ON instead of BUG in alb_upper_dev_walk

From: Jay Vosburgh <[email-masked]>
Date: Wed, 15 Nov 2023 12:34:09 -0800

Simon Horman <[email-masked]> wrote:

>On Wed, Nov 15, 2023 at 03:22:39PM +0100, Jiri Pirko wrote:
>> Wed, Nov 15, 2023 at 12:55:37PM CET, [email-masked] wrote:
>> >If failed to allocate "tags" or could not find the final upper device from
>> >start_dev's upper list in bond_verify_device_path(), only the loopback
>> >detection of the current upper device should be affected, and the system is
>> >no need to be panic.
>> >
>> >Signed-off-by: Zhengchao Shao <[email-masked]>
>> >---
>> >v3: return -ENOMEM instead of zero to stop walk
>> >v2: use WARN_ON_ONCE instead of WARN_ON
>> 
>> Yet the WARN_ON is back :O
>
>Hi Jiri,
>
>I think the suggestion was to either:
>
>1. WARN_ON_ONCE(); return 0;      <= this was v2
>2. WARN_ON(); return -ESOMETHING; <= this is v3
>(But not, WARN_ON(); return 0;    <= this was v1)
>
>And after v2 it was determined that the approach taken here in v3 is
>preferred.
>
>So I think this patch is consistent with the feedback given by Jay
>in his reviews so far.

	Sigh, the more I look the more complicated this gets.
	
	Anyway, I was previously thinking we're ok with WARN_ON if the
return is non-zero to terminate the device walk.  The bond itself will
automatically call alb_upper_dev_walk at most once per second.

	However, user space could do something like continuously change
the MAC address of the bond or initiate a failover in order to trigger a
call to alb_upper_dev_walk.  This won't be rate limited, and if the
allocations there repeatedly fail, it would always trigger the WARN_ON.

	So, I'm thinking now that instead of WARN_anything, we should
instead use something like

net_err_ratelimited("%s: %s: allocation failure\n", start_dev->name, __func__);

	in bond_verify_device_path, and alb_upper_dev_walk doesn't do
any WARN at all, and returns failure (non-zero).
	
	This is consistent with other similar allocation failures.

	-J

>> >---
>> > drivers/net/bonding/bond_alb.c | 6 ++++--
>> > 1 file changed, 4 insertions(+), 2 deletions(-)
>> >
>> >diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>> >index dc2c7b979656..21f1cb8e453b 100644
>> >--- a/drivers/net/bonding/bond_alb.c
>> >+++ b/drivers/net/bonding/bond_alb.c
>> >@@ -984,8 +984,10 @@ static int alb_upper_dev_walk(struct net_device *upper,
>> > 	 */
>> > 	if (netif_is_macvlan(upper) && !strict_match) {
>> > 		tags = bond_verify_device_path(bond->dev, upper, 0);
>> >-		if (IS_ERR_OR_NULL(tags))
>> >-			BUG();
>> >+		if (IS_ERR_OR_NULL(tags)) {
>> >+			WARN_ON(1);
>> >+			return -ENOMEM;
>> >+		}
>> > 		alb_send_lp_vid(slave, upper->dev_addr,
>> > 				tags[0].vlan_proto, tags[0].vlan_id);
>> > 		kfree(tags);
>> >-- 
>> >2.34.1
>> >
>> >
>> 
>

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