Message-ID: <06fa1aec-d9a6-3ca7-8849-a1656349ab83@oracle.com>
Date:   Wed, 27 Mar 2019 16:44:19 -0700
From:   si-wei liu <si-wei.liu@...cle.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     mst@...hat.com, sridhar.samudrala@...el.com,
        stephen@...workplumber.org, davem@...emloft.net, kubakici@...pl,
        alexander.duyck@...il.com, netdev@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, liran.alon@...cle.com,
        boris.ostrovsky@...cle.com, vijay.balakrishna@...cle.com
Subject: Re: [PATCH net v3] failover: allow name change on IFF_UP slave
 interfaces



On 3/27/2019 4:11 AM, Jiri Pirko wrote:
> Wed, Mar 27, 2019 at 12:48:13AM CET, si-wei.liu@...cle.com wrote:
>> When a netdev appears through hot plug then gets enslaved by a failover
>> master that is already up and running, the slave will be opened
>> right away after getting enslaved. Today there's a race that userspace
>> (udev) may fail to rename the slave if the kernel (net_failover)
>> opens the slave earlier than when the userspace rename happens.
>> Unlike bond or team, the primary slave of failover can't be renamed by
>> userspace ahead of time, since the kernel initiated auto-enslavement is
>> unable to, or rather, is never meant to be synchronized with the rename
>> request from userspace.
>>
>> As the failover slave interfaces are not designed to be operated
>> directly by userspace apps: IP configuration, filter rules with
>> regard to network traffic passing and etc., should all be done on master
>> interface. In general, userspace apps only care about the
>> name of master interface, while slave names are less important as long
>> as admin users can see reliable names that may carry
>> other information describing the netdev. For e.g., they can infer that
>> "ens3nsby" is a standby slave of "ens3", while for a
>> name like "eth0" they can't tell which master it belongs to.
>>
>> Historically the name of IFF_UP interface can't be changed because
>> there might be admin script or management software that is already
>> relying on such behavior and assumes that the slave name can't be
>> changed once UP. But failover is special: with the in-kernel
>> auto-enslavement mechanism, the userspace expectation for device
>> enumeration and bring-up order is already broken. Previously initramfs
>> and various userspace config tools were modified to bypass failover
>> slaves because of auto-enslavement and duplicate MAC address. Similarly,
>> in case that users care about seeing reliable slave name, the new type
>> of failover slaves needs to be taken care of specifically in userspace
>> anyway.
>>
>> It's less risky to lift up the rename restriction on failover slave
>> which is already UP. Although it's possible this change may potentially
>> break userspace component (most likely configuration scripts or
>> management software) that assumes slave name can't be changed while
>> UP, it's relatively a limited and controllable set among all userspace
>> components, which can be fixed specifically to listen for the rename
>> and/or link down/up events on failover slaves. Userspace component
>> interacting with slaves is expected to be changed to operate on failover
>> master interface instead, as the failover slave is dynamic in nature
>> which may come and go at any point.  The goal is to make the role of
>> failover slaves less relevant, and userspace components should only
>> deal with failover master in the long run.
>>
>> Fixes: 30c8bd5aa8b2 ("net: Introduce generic failover module")
>> Signed-off-by: Si-Wei Liu <si-wei.liu@...cle.com>
>> Reviewed-by: Liran Alon <liran.alon@...cle.com>
>>
>> --
>> v1 -> v2:
>> - Drop configurable module parameter (Sridhar)
>>
>> v2 -> v3:
>> - Drop additional IFF_SLAVE_RENAME_OK flag (Sridhar)
>> - Send down and up events around rename (Michael S. Tsirkin)
>> ---
>> net/core/dev.c | 37 ++++++++++++++++++++++++++++++++++---
>> 1 file changed, 34 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 722d50d..3e0cd80 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1171,6 +1171,7 @@ int dev_get_valid_name(struct net *net, struct net_device *dev,
>> int dev_change_name(struct net_device *dev, const char *newname)
>> {
>> 	unsigned char old_assign_type;
>> +	bool reopen_needed = false;
>> 	char oldname[IFNAMSIZ];
>> 	int err = 0;
>> 	int ret;
>> @@ -1180,8 +1181,24 @@ int dev_change_name(struct net_device *dev, const char *newname)
>> 	BUG_ON(!dev_net(dev));
>>
>> 	net = dev_net(dev);
>> -	if (dev->flags & IFF_UP)
>> -		return -EBUSY;
>> +
>> +	/* Allow failover slave to rename even when
>> +	 * it is up and running.
>> +	 *
>> +	 * Failover slaves are special, since userspace
>> +	 * might rename the slave after the interface
>> +	 * has been brought up and running due to
>> +	 * auto-enslavement.
>> +	 *
>> +	 * Failover users don't actually care about slave
>> +	 * name change, as they are only expected to operate
>> +	 * on master interface directly.
>> +	 */
>> +	if (dev->flags & IFF_UP) {
>> +		if (likely(!(dev->priv_flags & IFF_FAILOVER_SLAVE)))
>> +			return -EBUSY;
>> +		reopen_needed = true;
>> +	}
>>
>> 	write_seqcount_begin(&devnet_rename_seq);
>>
>> @@ -1198,6 +1215,9 @@ int dev_change_name(struct net_device *dev, const char *newname)
>> 		return err;
>> 	}
>>
>> +	if (reopen_needed)
>> +		dev_close(dev);
> Ugh. Don't dev_close/dev_open on name change.
See my response to Michael and Stephen. What's your suggestion then?
>
>> +
>> 	if (oldname[0] && !strchr(oldname, '%'))
>> 		netdev_info(dev, "renamed from %s\n", oldname);
>>
>> @@ -1210,7 +1230,9 @@ int dev_change_name(struct net_device *dev, const char *newname)
>> 		memcpy(dev->name, oldname, IFNAMSIZ);
>> 		dev->name_assign_type = old_assign_type;
>> 		write_seqcount_end(&devnet_rename_seq);
>> -		return ret;
>> +		if (err >= 0)
>> +			err = ret;
>> +		goto reopen;
>> 	}
>>
>> 	write_seqcount_end(&devnet_rename_seq);
>> @@ -1246,6 +1268,15 @@ int dev_change_name(struct net_device *dev, const char *newname)
>> 		}
>> 	}
>>
>> +reopen:
>> +	if (reopen_needed) {
>> +		ret = dev_open(dev);
>> +		if (ret) {
>> +			pr_err("%s: reopen device failed: %d\n",
>> +			       dev->name, ret);
>> +		}
>> +	}
>> +
>> 	return err;
>> }
>>
>> -- 
>> 1.8.3.1
>>

Powered by blists - more mailing lists