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Date: Thu, 23 Jan 2014 22:56:15 +0100
From: Veaceslav Falico <vfalico@...hat.com>
To: Jay Vosburgh <fubar@...ibm.com>
Cc: netdev@...r.kernel.org, Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH v2 net-next 2/2] bonding: restructure locking of
bond_ab_arp_probe()
On Thu, Jan 23, 2014 at 11:25:38AM -0800, Jay Vosburgh wrote:
>Veaceslav Falico <vfalico@...hat.com> wrote:
>
>>Currently we're calling it from under RCU context, however we're using some
>>functions that require rtnl to be held.
>>
>>Fix this by restructuring the locking - don't call it under any locks,
>>aquire rcu_read_lock() if we're sending _only_ (i.e. we have the active
>>slave present), and use rtnl locking otherwise - if we need to modify
>>(in)active flags of a slave.
>>
>>CC: Jay Vosburgh <fubar@...ibm.com>
>>CC: Andy Gospodarek <andy@...yhouse.net>
>>Signed-off-by: Veaceslav Falico <vfalico@...hat.com>
>>---
>> drivers/net/bonding/bond_main.c | 38 ++++++++++++++++++++++++--------------
>> 1 file changed, 24 insertions(+), 14 deletions(-)
>>
>>diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
>>index 22d8b69..f879e9e 100644
>>--- a/drivers/net/bonding/bond_main.c
>>+++ b/drivers/net/bonding/bond_main.c
>>@@ -2605,11 +2605,14 @@ do_failover:
>> static void bond_ab_arp_probe(struct bonding *bond)
>> {
>> struct slave *slave, *before = NULL, *new_slave = NULL,
>>- *curr_arp_slave = rcu_dereference(bond->current_arp_slave),
>>- *curr_active_slave = rcu_dereference(bond->curr_active_slave);
>>+ *curr_arp_slave, *curr_active_slave;
>> struct list_head *iter;
>> bool found = false;
>>
>>+ rcu_read_lock();
>>+ curr_arp_slave = rcu_dereference(bond->current_arp_slave);
>>+ curr_active_slave = rcu_dereference(bond->curr_active_slave);
>>+
>> if (curr_arp_slave && curr_active_slave)
>> pr_info("PROBE: c_arp %s && cas %s BAD\n",
>> curr_arp_slave->dev->name,
>>@@ -2617,23 +2620,31 @@ static void bond_ab_arp_probe(struct bonding *bond)
>>
>> if (curr_active_slave) {
>> bond_arp_send_all(bond, curr_active_slave);
>>+ rcu_read_unlock();
>> return;
>> }
>>+ rcu_read_unlock();
>>
>> /* if we don't have a curr_active_slave, search for the next available
>> * backup slave from the current_arp_slave and make it the candidate
>> * for becoming the curr_active_slave
>> */
>>
>>+ rtnl_lock();
>
> I don't believe we can unconditionally acquire RTNL here, as it
>may deadlock with bond_close's cancel_delayed_work_sync() calls (which
>occur under RTNL).
>
> I think I'd make this a rtnl_trylock, and if that fails, have
>the bond_ab_arp_probe function return non-zero as an indication for
>activebackup_arp_mon to change delta_in_ticks to 1. Changing the delta
>is just an optimization; without it, things will still work, but it will
>take longer to run the curr_arp_slave probe cycle.
True, missed this race. Will re-send once I'll fix it.
Thank you!
>
> -J
>
>>+ /* curr_arp_slave might have gone away */
>>+ curr_arp_slave = rcu_dereference(bond->current_arp_slave);
>>+
>> if (!curr_arp_slave) {
>>- curr_arp_slave = bond_first_slave_rcu(bond);
>>- if (!curr_arp_slave)
>>+ curr_arp_slave = bond_first_slave(bond);
>>+ if (!curr_arp_slave) {
>>+ rtnl_unlock();
>> return;
>>+ }
>> }
>>
>> bond_set_slave_inactive_flags(curr_arp_slave);
>>
>>- bond_for_each_slave_rcu(bond, slave, iter) {
>>+ bond_for_each_slave(bond, slave, iter) {
>> if (!found && !before && IS_UP(slave->dev))
>> before = slave;
>>
>>@@ -2663,21 +2674,24 @@ static void bond_ab_arp_probe(struct bonding *bond)
>> if (!new_slave && before)
>> new_slave = before;
>>
>>- if (!new_slave)
>>+ if (!new_slave) {
>>+ rtnl_unlock();
>> return;
>>+ }
>>
>> new_slave->link = BOND_LINK_BACK;
>> bond_set_slave_active_flags(new_slave);
>> bond_arp_send_all(bond, new_slave);
>> new_slave->jiffies = jiffies;
>> rcu_assign_pointer(bond->current_arp_slave, new_slave);
>>+ rtnl_unlock();
>> }
>>
>> static void bond_activebackup_arp_mon(struct work_struct *work)
>> {
>> struct bonding *bond = container_of(work, struct bonding,
>> arp_work.work);
>>- bool should_notify_peers = false;
>>+ bool should_notify_peers = false, should_commit = false;
>> int delta_in_ticks;
>>
>> delta_in_ticks = msecs_to_jiffies(bond->params.arp_interval);
>>@@ -2686,12 +2700,11 @@ static void bond_activebackup_arp_mon(struct work_struct *work)
>> goto re_arm;
>>
>> rcu_read_lock();
>>-
>> should_notify_peers = bond_should_notify_peers(bond);
>>+ should_commit = bond_ab_arp_inspect(bond);
>>+ rcu_read_unlock();
>>
>>- if (bond_ab_arp_inspect(bond)) {
>>- rcu_read_unlock();
>>-
>>+ if (should_commit) {
>> /* Race avoidance with bond_close flush of workqueue */
>> if (!rtnl_trylock()) {
>> delta_in_ticks = 1;
>>@@ -2700,13 +2713,10 @@ static void bond_activebackup_arp_mon(struct work_struct *work)
>> }
>>
>> bond_ab_arp_commit(bond);
>>-
>> rtnl_unlock();
>>- rcu_read_lock();
>> }
>>
>> bond_ab_arp_probe(bond);
>>- rcu_read_unlock();
>>
>> re_arm:
>> if (bond->params.arp_interval)
>>--
>>1.8.4
>>
>
>---
> -Jay Vosburgh, IBM Linux Technology Center, fubar@...ibm.com
>
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