netdev - Re: [patch net-next v4 5/7] bridge: defer switchdev fdb del call in fdb_del_external

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Message-ID: <20151013060542.GC2242@nanopsycho.orion>
Date:	Tue, 13 Oct 2015 08:05:42 +0200
From:	Jiri Pirko <jiri@...nulli.us>
To:	Scott Feldman <sfeldma@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Ido Schimmel <idosch@...lanox.com>,
	Elad Raz <eladr@...lanox.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
	"andrew@...n.ch" <andrew@...n.ch>,
	john fastabend <john.fastabend@...il.com>,
	David Laight <David.Laight@...lab.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: Re: [patch net-next v4 5/7] bridge: defer switchdev fdb del call in
 fdb_del_external_learn

Tue, Oct 13, 2015 at 05:28:20AM CEST, sfeldma@...il.com wrote:
>On Mon, Oct 12, 2015 at 11:03 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>> From: Jiri Pirko <jiri@...lanox.com>
>>
>> Since spinlock is held here, defer the switchdev operation.
>>
>> Signed-off-by: Jiri Pirko <jiri@...lanox.com>
>> ---
>>  net/bridge/br_fdb.c | 5 ++++-
>>  net/bridge/br_if.c  | 3 +++
>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
>> index f5e7da0..c88bd8e 100644
>> --- a/net/bridge/br_fdb.c
>> +++ b/net/bridge/br_fdb.c
>> @@ -134,7 +134,10 @@ static void fdb_del_hw_addr(struct net_bridge *br, const unsigned char *addr)
>>  static void fdb_del_external_learn(struct net_bridge_fdb_entry *f)
>>  {
>>         struct switchdev_obj_port_fdb fdb = {
>> -               .obj.id = SWITCHDEV_OBJ_ID_PORT_FDB,
>> +               .obj = {
>> +                       .id = SWITCHDEV_OBJ_ID_PORT_FDB,
>> +                       .flags = SWITCHDEV_F_DEFER,
>> +               },
>>                 .vid = f->vlan_id,
>>         };
>>
>> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
>> index 934cae9..09147cb 100644
>> --- a/net/bridge/br_if.c
>> +++ b/net/bridge/br_if.c
>> @@ -24,6 +24,7 @@
>>  #include <linux/slab.h>
>>  #include <net/sock.h>
>>  #include <linux/if_vlan.h>
>> +#include <net/switchdev.h>
>>
>>  #include "br_private.h"
>>
>> @@ -249,6 +250,8 @@ static void del_nbp(struct net_bridge_port *p)
>>         list_del_rcu(&p->list);
>>
>>         br_fdb_delete_by_port(br, p, 0, 1);
>> +       switchdev_flush_deferred();
>> +
>
>This potentially flushes other (valid) work on the deferred queue not
>related to FDB del.

flush_deferred is implemented by flush_workqueue. This enforces the
workqueue to be processed heve and sleeps until it is done. Nothing is
lost.


>
>I wonder if this flush step is necessary at all?  The work we deferred
>to delete the FDB entry can still happen after the port has been
>removed (del_nbp).  If the port driver/device find the FDB entry, then
>delete it, otherwise ignore it.

This step is necessary. Consider following scenario:

spin_lock
switchdev_schedule_deferred (workx)
spin_unlock
netdev_upper_dev_unlink
workx is executed-> driver op is executed.

But during netdev_upper_dev_unlink, resources may have been removed, so
the workx after that would fail (this happens in case of rocker).

So I added switchdev_flush_deferred so the caller may force to safely
process the pending work in right time, for example after he released
the spinlock (after br_fdb_delete_by_port in this case).
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