netdev - Re: [PATCH net-next,v4] bonding: return -ENOMEM instead of BUG in alb_upper_dev

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Date: Tue, 21 Nov 2023 12:41:21 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Zhengchao Shao <shaozhengchao@...wei.com>, netdev@...r.kernel.org, 
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org
Cc: j.vosburgh@...il.com, andy@...yhouse.net, weiyongjun1@...wei.com, 
	yuehaibing@...wei.com
Subject: Re: [PATCH net-next,v4] bonding: return -ENOMEM instead of BUG in
 alb_upper_dev_walk

On Sat, 2023-11-18 at 16:16 +0800, Zhengchao Shao 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.
> So return -ENOMEM in alb_upper_dev_walk to stop walking, print some warn
> information when failed to allocate memory for vlan tags in
> bond_verify_device_path.
> 
> I also think that the following function calls
> netdev_walk_all_upper_dev_rcu
> ---->>>alb_upper_dev_walk
> ---------->>>bond_verify_device_path
> > From this way, "end device" can eventually be obtained from "start device"
> in bond_verify_device_path, IS_ERR(tags) could be instead of
> IS_ERR_OR_NULL(tags) in alb_upper_dev_walk.
> 
> Signed-off-by: Zhengchao Shao <shaozhengchao@...wei.com>
> ---
> v4: print information instead of warn
> v3: return -ENOMEM instead of zero to stop walk
> v2: use WARN_ON_ONCE instead of WARN_ON
> ---
>  drivers/net/bonding/bond_alb.c  | 3 ++-
>  drivers/net/bonding/bond_main.c | 5 ++++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
> index dc2c7b979656..7edf0fd58c34 100644
> --- a/drivers/net/bonding/bond_alb.c
> +++ b/drivers/net/bonding/bond_alb.c
> @@ -985,7 +985,8 @@ 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();
> +			return -ENOMEM;
> +
>  		alb_send_lp_vid(slave, upper->dev_addr,
>  				tags[0].vlan_proto, tags[0].vlan_id);
>  		kfree(tags);
> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
> index 51d47eda1c87..1a40bd08f984 100644
> --- a/drivers/net/bonding/bond_main.c
> +++ b/drivers/net/bonding/bond_main.c
> @@ -2967,8 +2967,11 @@ struct bond_vlan_tag *bond_verify_device_path(struct net_device *start_dev,
>  
>  	if (start_dev == end_dev) {
>  		tags = kcalloc(level + 1, sizeof(*tags), GFP_ATOMIC);
> -		if (!tags)
> +		if (!tags) {
> +			net_err_ratelimited("%s: %s: Failed to allocate tags\n",
> +					    __func__, start_dev->name);

I'm sorry for the repeated back and forth, but checkpatch points out
that the above warning adds little value: if the memory allocation
fails, the mm layer will emit a lot warning comprising the backtrace.

I suggest to drop it, thanks!

Paolo