[PATCH v3 net-next 0/2] bonding: fix locking in bond_ab_arp_prob

[PATCH v3 net-next 0/2] bonding: fix locking in bond_ab_arp_prob

[Veaceslav Falico]

Hi,

After the latest patches, on every call of bond_ab_arp_probe() without an
active slave I see the following warning:

[    7.912314] RTNL: assertion failed at net/core/dev.c (4494)
...
[    7.922495]  [<ffffffff817acc6f>] dump_stack+0x51/0x72
[    7.923714]  [<ffffffff8168795e>] netdev_master_upper_dev_get+0x6e/0x70
[    7.924940]  [<ffffffff816a2a66>] rtnl_link_fill+0x116/0x260
[    7.926143]  [<ffffffff817acc6f>] ? dump_stack+0x51/0x72
[    7.927333]  [<ffffffff816a350c>] rtnl_fill_ifinfo+0x95c/0xb90
[    7.928529]  [<ffffffff8167af2b>] ? __kmalloc_reserve+0x3b/0xa0
[    7.929681]  [<ffffffff8167bfcf>] ? __alloc_skb+0x9f/0x1e0
[    7.930827]  [<ffffffff816a3b64>] rtmsg_ifinfo+0x84/0x100
[    7.931960]  [<ffffffffa00bca07>] bond_ab_arp_probe+0x1a7/0x370 [bonding]
[    7.933133]  [<ffffffffa00bcd78>] bond_activebackup_arp_mon+0x1a8/0x2f0 [bonding]
...

It happens because in bond_ab_arp_probe() we change the flags of a slave
without holding the RTNL lock.

To fix this - remove the useless curr_active_lock, RCUify it and lock RTNL
while changing the slave's flags. Also, remove bond_ab_arp_probe() from
under any locks in bond_ab_arp_mon().

CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
CC: netdev@vger.kernel.org
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>

---
 drivers/net/bonding/bond_main.c | 67 ++++++++++++++++++++++++-----------------
 1 file changed, 39 insertions(+), 28 deletions(-)

[PATCH v3 net-next 1/2] bonding: RCUify bond_ab_arp_probe

[Veaceslav Falico]

Currently bond_ab_arp_probe() is always called under rcu_read_lock(),
however to work with curr_active_slave we're still holding the
curr_slave_lock.

To remove that curr_slave_lock - rcu_dereference the bond's
curr_active_slave and use it further - so that we're sure the slave won't
go away, and we don't care if it will change in the meanwhile.

CC: Jay Vosburgh <fubar@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
---
 drivers/net/bonding/bond_main.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index a7db819..27e6fdd 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2605,25 +2605,21 @@ 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_arp_slave = rcu_dereference(bond->current_arp_slave),
+		     *curr_active_slave = rcu_dereference(bond->curr_active_slave);
 	struct list_head *iter;
 	bool found = false;
 
-	read_lock(&bond->curr_slave_lock);
-
-	if (curr_arp_slave && 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,
-			bond->curr_active_slave->dev->name);
+			curr_active_slave->dev->name);
 
-	if (bond->curr_active_slave) {
-		bond_arp_send_all(bond, bond->curr_active_slave);
-		read_unlock(&bond->curr_slave_lock);
+	if (curr_active_slave) {
+		bond_arp_send_all(bond, curr_active_slave);
 		return;
 	}
 
-	read_unlock(&bond->curr_slave_lock);
-
 	/* 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
-- 
1.8.4

[PATCH v3 net-next 2/2] bonding: restructure locking of bond_ab_arp_probe()

[Veaceslav Falico]

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@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
---

Notes:
    v2->v3:
    Use rtnl_trylock(), not to race with queue cancelling.
    
    v1->v2:
    Add two steps - one for sending/rcu, another for modifying/rtnl.

 drivers/net/bonding/bond_main.c | 57 ++++++++++++++++++++++++++---------------
 1 file changed, 36 insertions(+), 21 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 27e6fdd..dd75615 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -2599,17 +2599,18 @@ do_failover:
 
 /*
  * Send ARP probes for active-backup mode ARP monitor.
- *
- * Called with rcu_read_lock hold.
  */
-static void bond_ab_arp_probe(struct bonding *bond)
+static bool 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 +2618,32 @@ static void bond_ab_arp_probe(struct bonding *bond)
 
 	if (curr_active_slave) {
 		bond_arp_send_all(bond, curr_active_slave);
-		return;
+		rcu_read_unlock();
+		return true;
 	}
+	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
 	 */
 
+	if (!rtnl_trylock())
+		return false;
+	/* curr_arp_slave might have gone away */
+	curr_arp_slave = ACCESS_ONCE(bond->current_arp_slave);
+
 	if (!curr_arp_slave) {
-		curr_arp_slave = bond_first_slave_rcu(bond);
-		if (!curr_arp_slave)
-			return;
+		curr_arp_slave = bond_first_slave(bond);
+		if (!curr_arp_slave) {
+			rtnl_unlock();
+			return true;
+		}
 	}
 
 	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 +2673,26 @@ static void bond_ab_arp_probe(struct bonding *bond)
 	if (!new_slave && before)
 		new_slave = before;
 
-	if (!new_slave)
-		return;
+	if (!new_slave) {
+		rtnl_unlock();
+		return true;
+	}
 
 	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();
+
+	return true;
 }
 
 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 +2701,11 @@ 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 +2714,14 @@ 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();
+	if (!bond_ab_arp_probe(bond)) {
+		/* rtnl locking failed, re-arm */
+		delta_in_ticks = 1;
+		should_notify_peers = false;
+	}
 
 re_arm:
 	if (bond->params.arp_interval)
-- 
1.8.4

Re: [PATCH v3 net-next 0/2] bonding: fix locking in bond_ab_arp_prob

[David Miller]

From: Veaceslav Falico <vfalico@redhat.com>
Date: Mon, 27 Jan 2014 14:37:30 +0100

> After the latest patches, on every call of bond_ab_arp_probe() without an
> active slave I see the following warning:
...
> It happens because in bond_ab_arp_probe() we change the flags of a slave
> without holding the RTNL lock.
> 
> To fix this - remove the useless curr_active_lock, RCUify it and lock RTNL
> while changing the slave's flags. Also, remove bond_ab_arp_probe() from
> under any locks in bond_ab_arp_mon().
> 
> CC: Jay Vosburgh <fubar@us.ibm.com>
> CC: Andy Gospodarek <andy@greyhouse.net>
> CC: netdev@vger.kernel.org
> Signed-off-by: Veaceslav Falico <vfalico@redhat.com>

Series applied, thanks Vaeceslav.

Re: [PATCH v3 net-next 2/2] bonding: restructure locking of bond_ab_arp_probe()

[Veaceslav Falico]

On Mon, Jan 27, 2014 at 02:33:33PM +0100, Veaceslav Falico 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@us.ibm.com>
>CC: Andy Gospodarek <andy@greyhouse.net>
>Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
>---
>
>Notes:
>    v2->v3:
>    Use rtnl_trylock(), not to race with queue cancelling.
>
>    v1->v2:
>    Add two steps - one for sending/rcu, another for modifying/rtnl.
>
> 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 27e6fdd..7de0256 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();

Right, git commit --amend would be great after git add...

Sorry, forgot to actually commit changes, will re-send.

>+	/* 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
>

[PATCH v3 net-next 2/2] bonding: restructure locking of bond_ab_arp_probe()

[Veaceslav Falico]

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@us.ibm.com>
CC: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Veaceslav Falico <vfalico@redhat.com>
---

Notes:
    v2->v3:
    Use rtnl_trylock(), not to race with queue cancelling.
    
    v1->v2:
    Add two steps - one for sending/rcu, another for modifying/rtnl.

 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 27e6fdd..7de0256 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();
+	/* 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